THIRD AMENDMENT OF LEASE

         THIS THIRD  AMENDMENT  OF LEASE dated as of July 26, 1999  between LONG
GATE LLC ("Landlord") and HELIX TECHNOLOGY CORPORATION ("Tenant").

                                   BACKGROUND

         Landlord is the current  Landlord (as  successor to Mansfield  Commerce
Realty  Trust) and Tenant is the Tenant  under a Lease dated as of July 24, 1984
as amended by First  Amendment to Lease dated May 9, 1989 and Amendment to Lease
(the  "Second  Amendment")  dated as of  September  19,  1994 (the  "Lease")  of
premises  at 375 Forbes  Boulevard,  Mansfield,  Massachusetts.  The term of the
Lease will expire on September 30, 1999.  The parties  desire to extend the term
of the Lease and to otherwise amend the Lease, all as hereinafter set forth.

                                   WITNESSETH

         NOW THEREFORE, Landlord and Tenant hereby agree as follows:

1. The term of the Lease is hereby extended for the period commencing on October
1, 1999 and  terminating on September 30, 2004.  Except as herein  amended,  all
terms of the Lease shall continue in full force and effect.

2. The fixed rent payable under  Section 5(a) of the Lease shall be  $430,252.50
from October 1, 1999 through  September  30,  2000;  $444,594.50  per annum from
October 1, 2000 through  September  30,  2002;  and  $458,936.00  per annum from
October 1, 2002 through  September  30, 2004.  Such fixed rents shall be paid in
advance in equal monthly installments on the first day of each month.

3.  Section 4 of the Second  Amendment  is hereby  deleted from the Lease in its
entirety.

4.  Tenant  shall have one (1) option to extend the term of the Lease for a five
(5) year period (the "Option Period"),  provided (a) Tenant shall give notice to
Landlord of its exercise of such option prior to October 1, 2003, (b) no default
beyond any applicable  grace period in the obligations of Tenant under the Lease
shall exist at the time such notice is given and (c) Tenant  shall not have been
in default under the Lease beyond any  applicable  grace period on more than two
(2) occasions prior to the  commencement of the Option Period.  All of the terms
and provisions of the Lease shall be applicable  during the Option Period except
that (a) Tenant  shall have no option to extend the term of the Lease beyond the
Option Period and (b) the fixed rent payable under Section 5(a) of the Lease for
the Option  Period  shall be the  greater of (i) the fixed  rent  payable  under
Section 5(a) of the Lease for the year ending  September 30, 2004 or (ii) 95% of
the Market Rent, as defined below, as of the first day of the Option Period.
<PAGE>

         "Market Rent" shall be computed as of the  applicable  date at the then
current  rentals  being charged to new tenants for  comparable  space located in
comparable  buildings in the industrial  park in which the Premises are located,
taking into account and giving effect to, in determining comparability,  without
limitation,  such considerations as size, location and condition of premises and
lease term.

         Landlord shall initially  designate  Market Rent and shall furnish data
in  support  of such  designation.  If Tenant  shall  disagree  with  Landlord's
designation  of the Market  Rent,  then Tenant  shall have the right,  by notice
given  within  fourteen  (14) days  after  Tenant  shall have been  notified  of
Landlord's  designation,  to submit such Market Rent to  arbitration as follows.
Market Rent shall be determined by arbitrators, one chosen by Tenant, one chosen
by  Landlord  and a  third  selected,  if  necessary,  as  below  provided.  All
arbitrators  selected  under  this  Section  shall be  experienced  real  estate
appraisers  with  substantial  experience with properties in the vicinity of the
Premises.  If within  fourteen (14) days after Tenant's notice the parties shall
agree  upon a  single  arbitrator  or if one  party  shall  fail  to  select  an
arbitrator,  the arbitrator  selected by the other shall be the sole arbitrator,
and Market Rent shall be determined by such  arbitrator.  The unanimous  written
decision  of the two first  chosen (or the  decision  of the first,  if a second
arbitrator  is not  chosen)  without  selection  and  participation  of a  third
arbitrator,  or  otherwise  the  written  decision  of a  majority  of the three
arbitrators  chosen and selected as provided  herein,  shall be  conclusive  and
binding  upon  Landlord  and Tenant.  Landlord  and Tenant shall each notify the
other of its chosen  arbitrator within fourteen (14) days following the call for
arbitration,  and,  unless  such two  arbitrators  shall have  either  reached a
unanimous  decision  within thirty (30) days after their  designation or jointly
selected a third  arbitrator,  they shall so notify  the then  President  of the
local Real Estate Board and request him to select an impartial third  arbitrator
to act hereunder.  Such third arbitrator and the first two chosen shall hear the
parties and their  evidence and render their  decision  within  thirty (30) days
following the conclusion of such hearing and notify Landlord and Tenant thereof.
Landlord  and Tenant  shall bear the  expense of the third  arbitrator  (if any)
equally.  If the  dispute  between  the parties as to Market Rent shall not have
been resolved before the  commencement of Tenant's  obligation to pay rent based
upon  Market  Rent,  then  Tenant  shall pay rent  based  upon the  Market  Rent
designated  by  Landlord  until  either the  agreement  of the parties as to the
Market  Rent or the  decision of the  arbitrators,  as the case may be, at which
time Tenant  shall pay any  underpayment  of rent to Landlord or Landlord  shall
refund any overpayment of rent to Tenant.


<PAGE>



         WITNESS the execution hereof as an instrument under seal as of the date
first above written.

                                  LANDLORD:
                                  LONG GATE LLC


                                  By:      /s/ Cynthia Sarver
                                           ------------------------------
                                           Cynthia Sarver
                                           Its VP



                                  TENANT:
                                  HELIX TECHNOLOGY CORPORATION



                                  By:      /s/Michael El-Hillow
                                           ------------------------------
                                           Michael El-Hillow
                                           Its Chief Financial Officer