Exhibit 10.12F

THIRD AMENDMENT TO REVOLVING CREDIT AGREEMENT

THIS THIRD AMENDMENT TO REVOLVING CREDIT AGREEMENT(this "Amendment") made as of the 15th day of March, 2005 by
and amongAMERIVEST PROPERTIES INC.,a Maryland corporation (the "Borrower"),AMERIVEST
CHATEAU INC.,a Texas corporation ("Chateau") andAMERIVEST GREENHILL INC.,a Texas corporation ("Greenhill";
Chateau and Greenhill are sometimes hereinafter referred to individually as "Guarantor" and collectively as "Guarantors"),KEYBANK NATIONAL ASSOCIATION,
a national banking association ("KeyBank"),U.S. BANK NATIONAL ASSOCIATION("US Bank"; KeyBank, US Bank and the other lenders which may hereafter become
a party to the Loan Agreement (as hereinafter defined) are hereinafter referred to collectively as the "Lenders") andKEYBANK NATIONAL ASSOCIATION,a
national banking association, as agent (the "Agent").

W I T N E S S E T H:

WHEREAS,the Borrower, Fleet National Bank ("Fleet") and Fleet, as Agent ("Original Agent") entered into that
certain Revolving Credit Agreement dated November 12, 2002, as amended by that certain First Amendment to Revolving Credit Agreement dated February 6, 2003 and that certain Second
Amendment to Revolving Credit Agreement dated March 16, 2004 (as amended, the "Loan Agreement"); and

WHEREAS,KeyBank has acquired the interests of Fleet under the Credit Agreement pursuant to an Assignment and Acceptance dated
October 4, 2004;

WHEREAS,Original Agent has resigned as "Agent" under the Credit Agreement and the Agent has been appointed as successor
Agent under the Credit Agreement; and

WHEREAS,Chateau executed and delivered to the Agent a Guaranty dated as of November 25, 2002 (the "Chateau Guaranty"); and

WHEREAS,Greenhill executed and delivered to the Agent a Guaranty dated December 3, 2003 (the "Greenhill Guaranty"; the Chateau
Guaranty and the Greenhill Guaranty are hereinafter referred to collectively as the "Guaranties"); and

WHEREAS,the Borrower, the Lenders and the Agent have agreed to modify certain provisions of the Loan Agreement; and

WHEREAS,as a condition to such modification, the Agent and the Lenders have required that the Borrower and the Guarantors execute this
Amendment; and

NOW, THEREFORE,for and in consideration of the sum of TEN and NO/100 DOLLARS ($10.00), and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, the parties hereto do hereby covenant and agree as follows:

1.Definitions.    All the terms used herein which are not otherwise defined herein shall have the meanings set
forth in the Loan Agreement.

2.Modification Fee.    The Borrower hereby agrees to pay to the Agent, for the account of US Bank, a
non-refundable cash fee (the "Modification Fee") in the amount of $40,000 in the aggregate, which Modification Fee shall be fully earned when paid and non-refundable under any
circumstances.

3.Modification of the Loan Agreement.    The Borrower, the Agent and the Lenders do hereby modify and amend the
Loan Agreement as follows:



4.Waiver.    The Agent and the Lender do hereby waive the Default by Borrower of compliance with the covenants set
forth in §§9.3, 9.4 and 9.5 of the Loan Agreement for the fiscal quarter ending December 31, 2004. The Agent and the Lenders have made no agreement, and are in no way
obligated, to grant any future extension, waiver, indulgence or consent.

5.References to Loan Agreement.    All references in the Loan Documents to the Loan Agreement shall be deemed a
reference to the Loan Agreement as modified and amended herein.

6.Consent of Guarantors.    By execution of this Amendment, each Guarantor hereby expressly consents to the
modification and amendment to the Loan Agreement as set forth herein, and the Borrower and the Guarantors hereby acknowledge, represent and agree that the Loan Documents


(including without limitation the Guaranties) remain in full force and effect and constitute the valid and legally binding obligations of the Borrower and the Guarantors enforceable against such
Persons in accordance with their respective terms, and that the execution and delivery of this Amendment and any other modification documents do not constitute, and shall not be deemed to constitute,
a release, waiver or satisfaction of Borrower's or the Guarantors' obligations under the Loan Documents (including, without limitation, the Guaranties).

7.Representations.    Borrower and each Guarantor represents and warrants to Agent and the Lenders as follows:



8.No Default.    By execution hereof, the Borrower and each of the Guarantors certifies that each such Person is
and will be in compliance with all covenants under the Loan Documents after the execution and delivery of this Amendment, and that no Default or Event of Default has occurred and is continuing under
the Loan Documents, as amended by this Amendment.

9.Waiver of Claims.    The Borrower and each Guarantor acknowledges, represents and agrees that none of such
Persons has any defenses, setoffs, claims, counterclaims or causes of action of any kind or nature whatsoever with respect to the Loan Documents, the administration or funding of the Loans or with
respect to any acts or omissions of Agent or the Lenders, or any past or present officers, agents or employees of the Agent or the Lenders, and each of such Persons does hereby expressly waive,
release and relinquish any and all such defenses, setoffs, claims, counterclaims and causes of action, if any.

10.Ratification.    Except as hereinabove set forth, all terms, covenants and provisions of the Loan Documents,
including, without limitation, the Loan Agreement, remain unaltered and in full force and effect, and the parties hereto do hereby expressly ratify and confirm, the Loan Documents and the Loan
Agreement as modified and amended herein. Nothing in this Amendment shall be deemed or construed to constitute, and there has not otherwise occurred, a novation, cancellation, satisfaction,


release, extinguishment or substitution of the indebtedness evidenced by the Notes or the other obligations of the Borrower and the Guarantors under the Loan Documents.

11.Effective Date.    This Amendment shall be deemed effective and in full force and effect upon the execution and
delivery of this Amendment by the Borrower, the Guarantors, the Agent and the Lenders.

12.Amendment as Loan Document.    This Amendment shall constitute a Loan Document.

13.Counterparts.    This Amendment may be executed in any number of counterparts which shall together constitute
but one and the same agreement.

14.Miscellaneous.    This Amendment shall be construed and enforced in accordance with the laws of The
Commonwealth of Massachusetts. This Amendment shall be binding upon and shall inure to the benefit of the parties hereto and their respective permitted successors,
successors-in-title and assigns as provided in the Loan Agreement and the Guaranties.

[Remainder of Page Intentionally Left Blank; Signatures on Following Page]



IN WITNESS WHEREOF, the parties hereto have hereto set their hands and affixed their seals as of the day and year first above written.

| |  | BORROWER:                                        
| |  | -------------------------------------------------
| |  | AMERIVEST PROPERTIES INC., a Maryland corporation
| |  | By:                                              
| |  | Name:                                            
| |  | Title:                                           
| |  | [CORPORATE SEAL]                                 
| |  | GUARANTORS:                                      
| |  | AMERIVEST CHATEAU INC., a Texas corporation      
| |  | By:                                              
| |  | Name:                                            
| |  | Title:                                           
| |  | [CORPORATE SEAL]                                 
| |  | AMERIVEST GREENHILL INC., a Texas corporation    
| |  | By:                                              
| |  | Name:                                            
| |  | Title:                                           
| |  | [CORPORATE SEAL]                                 



| |  | LENDERS:                                                              
| |  | ----------------------------------------------------------------------
| |  | KEYBANK NATIONAL ASSOCIATION, a national banking association          
| |  | By:                                                                   
| |  | Name:                                                                 
| |  | Title:                                                                
| |  | U.S. BANK NATIONAL ASSOCIATION                                        
| |  | By:                                                                   
| |  | Name:                                                                 
| |  | Title:                                                                
| |  | AGENT:                                                                
| |  | KEYBANK NATIONAL ASSOCIATION, a national banking association, as Agent
| |  | By:                                                                   
| |  | Name:                                                                 
| |  | Title:                                                                



Schedule I
to
Third Amendment to Revolving Credit Agreement

Existing Indebtedness

[List]



Debt Summary

|                                                      |                               |                                                      |                                                                       |            |            | March 15, 2005 |           
|----------------------------------------------------- | ----------------------------- | ---------------------------------------------------- | --------------------------------------------------------------------- | ---------- | ---------- | -------------- | ----------
|
|Fixed Rate                                           |                               |                                                      |                                                                       |            |            |                |           
|Teachers Insurance and Annuity Association of America |                               | AmeriVest Plaza at Inverness                         |                                                                       | 1/10/2006  |            | $              | 14,370,197
|Greenwich Capital Financial Products                  |                               | Parkway Centre II Centerra
Southwest Gas Building    |                                                                       | 10/1/2008  |            |                | 37,910,204
|Metropolitan Life Insurance Company                   |                               | Parkway Centre III                                   |                                                                       | 9/10/2009  |            |                | 15,070,941
|Allstate Life Insurance Company                       |                               | Financial Plaza                                      |                                                                       | 10/5/2010  |            |                | 24,045,098
|Southern Farm Bureau Life Insurance Company           |                               | Scottsdale Norte                                     |                                                                       | 4/1/2011   |            |                | 6,553,667 
|J. P. Morgan Chase                                    |                               | Hackberry View1st                                   |                                                                       | 9/1/2012   |            |                | 11,388,359
|J. P. Morgan Chase                                    |                               | Hackberry View2nd(2)                                |                                                                       | 9/1/2012   |            |                | 960,405   
|Teachers Insurance and Annuity Association of America |                               | Sheridan Center Arrowhead Fountains
Kellogg Building |                                                                       | 1/1/2013   |            |                | 28,733,061
|Allstate Life Insurance Company                       |                               | Camelback1st                                        |                                                                       | 9/5/2014   |            |                | 15,855,852
|Allstate Life Insurance Company                       |                               | Camelback2nd                                        |                                                                       | 9/5/2014   |            |                | 4,954,954 
|Security Life of Denver Insurance Company             |                               | Keystone Office Park1st                             |                                                                       | 5/1/2022   |            |                | 4,207,994 
|Security Life of Denver Insurance Company             |                               | Keystone Office Park2nd                             |                                                                       | 5/1/2022   |            |                | 471,308   
|GEMSA                                                 |                               | Hampton Court                                        |                                                                       | 11/1/2007  |            |                | 7,900,000 
|                                                      |                               |                                                      |                                                                       |            |            |                |           
|                                                      |                               | Subtotal                                             |                                                                       |            |            |                |           
|                                                      |                               |                                                      |                                                                       |            |            |                |           
|Variable Rate                                        |                               |                                                      |                                                                       |            |            |                |           
|KeyBank National Association                         |                               | Chateau Plaza                                        |                                                                       | 11/12/2005 |            | $              | 32,900,000
|                                                      | Senior Secured Line of Credit |                                                      | Greenhill Park                                                        |            |            |                |           
|KeyBank National Association                         |                               |                                                      |                                                                       |            |            |                |           
|                                                      | Unsecured Line of Credit      |                                                      | Unsecured                                                             |            | 11/12/2007 |                |           
|                                                      |                               |                                                      |                                                                       |            |            |                |           
|                                                      |                               | Subtotal                                             |                                                                       |            |            |                |           
|                                                      |                               |                                                      |                                                                       |            |            |                |           
|Other notes payable                                  |                               |                                                      |                                                                       |            |            |                |           
|Lease Capital Corporation                             |                               | Phone system                                         |                                                                       | 10/31/2007 |            |                | 59,240    
|                                                      |                               |                                                      |                                                                       |            |            |                |           
|                                                      |                               | Subtotal                                             |                                                                       |            |            |                |           
|                                                      |                               |                                                      |                                                                       |            |            |                |           
|                                                      |                               |                                                      | Total debt, excluding "liabilitiesheld for sale'                     |            |            |                |           
|                                                      |                               |                                                      |                                                                       |            |            |                |           
|Liabilitiesheld for sale                             |                               |                                                      |                                                                       |            |            |                |           
|Jefferson Pilot                                       |                               | Texas Bank Buildings                                 |                                                                       |            |            | $              |          
|                                                      |                               |                                                      |                                                                       |            |            |                |           
|                                                      |                               |                                                      | Total including mortgage loan included in "liabilitiesheld for sale' |            |            |                |           
|                                                      |                               |                                                      |                                                                       |            |            |                |           

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