In an interview, Wren said that Omnicom has "no skeletons in the closet".
He said: "The integrity of this company, its management, its board of directors and its employees is paramount to everything we do, just as it always has been."
Omnicom's share price has plummeted over the last two weeks after, first, rumours of a negative news story and then the publication of an article in the Wall Street Journal questioning its account practices.
The turmoil has already sparked legal action, with New York law firm Wolf Popper last week launching a class action against Omnicom. Wolf has been joined by a second law firm, Baltimore-based Charles J Piven, PA, which has also started a class action suit on behalf of shareholders who bought stock between April 25 2000 and June 11 2002.
The seeds for the current furore were sowed by the resignation of Robert Callander from the Omnicom board of directors. Callander had been chairman of the audit committee and quit the company in May, reportedly because he was unhappy with the limited disclosure of the group's management to the audit committee, relating to internet assets.
Omnicom also switched auditors, dumping Andersen for KPMG.
Despite the lawsuits and a Wall Street-wide fall on shares, Omnicom managed to reclaim a little ground on Friday, when its shares closed up by $0.43, or 0.79%, at $50.05 -- almost half the value they were trading at in April.
Omnicom is the third-largest marketing company in the world, owning the BBDO Worldwide ad network and the Fleishman-Hillard public relations network.
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