The Denver-based company also said it may face sanctions or be forced to cut fees because of state and federal investigations.

Mark Whiston's resignation was not sought by regulators and was unrelated to any proposed settlements, Janus spokeswoman Shelley Petersen said. "It was his decision in consultation with the board," she said.

Whiston, named CEO 15 months ago, will be replaced by board chairman Steve Scheid, a former executive at Charles Schwab Corp.

Although analysts said Whiston was working to implement reforms, they noted that he was in charge during the time of the alleged improper trading. They applauded his decision to step down as a way to help bolster investor confidence.

"I just don't think Mark Whiston had the credibility to do what he needed to do or what he wanted to do," Morningstar equity analyst Rachel Barnard said. "I think it's the right move for Janus."

New York Attorney General Eliot Spitzer, the Securities and Exchange Commission, Colorado Attorney General Ken Salazar and others are investigating Janus policies and arrangements allowing market timing — a type of rapid, in-and-out trading that can skim profits from long-term fund shareholders.

The practice is legal, but Janus policies discouraged it. Regulators say for that reason, allowing it constituted securities fraud.

Whiston is the latest in a string of top executives who resigned or were forced out of mutual-funds companies as a result of the scandal. Some companies have agreed to settlements ranging from $40 million to $675 million.

Analyst Robert A. Lee of Keefe, Bruyette & Woods said the executive change was a way for Janus to move forward.