“Brian has made important contributions to Marsh's recovery over the past two years,” said Mr. Cherkasky. “Our long-term strategy is sound and a solid foundation has been built. That said, we now need a different set of leadership and operational skills to complete the successful transformation of Marsh.”

An MMC representative, Christine Walton, said the company has not set a timeline for finding a new CEO but plans to make the move as “expeditiously as possible.” The search for Mr. Storms' replacement will not be limited to within MMC, she added. “We want to make sure we have the right person for the job.”

According to analysts, the move underscores disorder at one of the world's three biggest insurance brokerages. Marsh has been struggling to reboot its operation and restore its former levels of revenue and profitability ever since the scandal over steering of customers and bid-rigging prompted the firm to give up lucrative, volume-based contingent commissions.

David Small, an analyst at Bear Steans, said the CEO's resignation follows management turmoil in the brokerage division, where the company has seen a number of management figures leave for other firms.

Mr. Small wrote that the moves are underscored by the brief departure of Tim Mahoney, CEO of North America for Marsh, who resigned to move to Integro, a landing spot for a number of top Marsh officers in the past–only to return on a counter offer–as a sign of the turmoil still rocking the firm.

Loss of market share to Aon and a number of disappointing earnings reports probably contributed to Mr. Storms' departure, Mr. Small speculated.

William Wilt, an analyst at Morgan Stanley, said in a note to investors that the turmoil at Marsh “could weigh on client relationships…in a relationship business,” suggesting that both Aon and Willis could gain market share at Marsh's expense.

Addressing comments from analysts concerning the turmoil at MMC, Ms. Walton said that as the brokerage has tried to transform itself into a leaner operation and refocus its business initiatives, it created “a lot of noise” and confusion among the rank and file.

The new CEO's focus will be to streamline the changes in the organization and let people get back to what they do best, which is “being the world's biggest insurance broker,” she said.

The departure of Mr. Storms sent the company's stock down 6 percent on Monday, Sept. 17, from its close on Sept. 14 of $26.18 to $24.60. It was the company's lowest closing price since Oct. 19, 2004, when the stock closed at $24.10 a share. The stock also reached its lowest point in over a year when it closed at $24.77 on Aug. 9, 2006.

The price drop was fueled by reports that Morgan Stanley and Citigroup had downgraded MMC.