Exhibit 31.1

RULE 13a-14(a)
CERTIFICATION IN ACCORDANCE WITH SECTION 302 OF THE
SARBANES-OXLEY ACT OF 2002

I, Joel F. Gemunder,
President and Chief Executive Officer of Omnicare, Inc. (the Company),
certify that:

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| | 1. | I have reviewed this
 report on Form 10-Q of the Company;                                                                                                                                                                                                                                                                         
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| | 2. | Based on my knowledge,
 this report does not contain any untrue statement of a material fact or omit
 to state a material fact necessary to make the statements made, in light of
 the circumstances under which such statements were made, not misleading with
 respect to the period covered by this report;                    
| |    |                                                                                                                                                                                                                                                                                                                                   
| | 3. | Based on my knowledge, the
 financial statements, and other financial information included in this
 report, fairly present in all material respects the financial condition,
 results of operations and cash flows of the Company as of, and for, the
 periods presented in this report;                                          
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| | 4. | The Companys other
 certifying officer and I are responsible for establishing and maintaining
 disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e)
 and 15d-15(e)) and internal control over financial reporting (as defined in
 Exchange Act Rules 13a-15(f) and 15d-15(f)) for the Company and have:
| |    |                                                                                                                                                                                                                                                                                                                                   
| |    | a)                                                                                                                                                                                                                                                                                                                                 | designed such disclosure
 controls and procedures, or caused such disclosure controls and procedures to
 be designed under our supervision, to ensure that material information
 relating to the Company, including its consolidated subsidiaries, is made
 known to us by others within those entities, particularly during the period
 in which this report is being prepared;
| |    |                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                 
| |    | b)                                                                                                                                                                                                                                                                                                                                 | designed such internal
 control over financial reporting, or caused such internal control over
 financial reporting to be designed under our supervision, to provide
 reasonable assurance regarding the reliability of financial reporting and the
 preparation of financial statements for external purposes in accordance with
 generally accepted accounting principles;    
| |    |                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                 
| |    | c)                                                                                                                                                                                                                                                                                                                                 | evaluated the
 effectiveness of the Companys disclosure controls and procedures and
 presented in this report our conclusions about the effectiveness of the
 disclosure controls and procedures, as of the end of the period covered by
 this report based on such evaluation; and                                                                                            
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| |    | d)                                                                                                                                                                                                                                                                                                                                 | disclosed in this report
 any change in the Companys internal control over financial reporting that
 occurred during the Companys most recent fiscal quarter that has materially
 affected, or is reasonably likely to materially affect, the Companys
 internal control over financial reporting; and                                                                       
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| | 5. | The Companys other
 certifying officer and I have disclosed, based on our most recent evaluation
 of internal control over financial reporting, to the Companys auditors and
 the audit committee of the Companys board of directors:                                                                                          
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| |    | a)                                                                                                                                                                                                                                                                                                                                 | all significant
 deficiencies and material weaknesses in the design or operation of internal
 control over financial reporting which are reasonably likely to adversely
 affect the Companys ability to record, process, summarize and report
 financial information; and                                                                                                      
| |    |                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                 
| |    | b)                                                                                                                                                                                                                                                                                                                                 | any fraud, whether or not
 material, that involves management or other employees who have a significant
 role in the Companys internal control over financial reporting.                                                                                                                                                                                                       

Date:
October 31, 2007

| |                                       
| | --------------------------------------
| | /s/ Joel F. Gemunder                  
| |                                       
| | Joel F. Gemunder                      
| | President and Chief
 Executive Officer

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