Biogen Inc.'s president and CEO, James Tobin, resigned unexpectedly after five years for what were described as personal reasons, and the company elected board chairman James Vincent to fill his positions.

"This was totally initiated by Jim [Tobin]," Vincent said in a conference call. "He decided to tender his resignation." The board "was shocked and surprised, and hoped he would change his mind," he added. Tobin also was a director.

"We don't intend any lurching changes here with our going-forward strategy," Vincent said. "We're having an excellent quarter, and expect to finish up an excellent year." Vincent said he does not intend to stay in the CEO position, which he held from 1985 to 1997, longer than a year or two. Vincent also served as president of the Cambridge, Mass.-based company, from 1985 to 1994, and led development of its flagship product, Avonex (interferon beta-1a).

Vincent said his goal is to promote current members of the management team into the higher positions.

He declined to provide further details about Tobin's departure. He said no severance element is involved, since Tobin left voluntarily.

Biogen's stock (NASDAQ:BGEN) closed Wednesday at $80, down $6.875. — Jim Shrine