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;                      
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|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:

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| | 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;
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| | 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;    
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| | 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
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| | 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.                                                                                                   

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|-------------------- | ---------------------------------------
|Date: August 9, 2007 |                                        
|                     |                                        
|                     | /s/ Joel F. Gemunder                   
|                     |                                        
|                     | Joel F. Gemunder                       
|                     | President and Chief
  Executive Officer

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