Guenter Verheugen said that because of the Social Democrats' "difficult situation" he was quitting as parliamentary whip to give the party leader, Rudolf Scharping, the chance to fill the post with someone who can "concentrate his whole powers" on the job. Mr Verheugen said he cannot do that because of his other duties.
The once-great party of the late Willy Brandt has been unable to oust Chancellor Helmut Kohl since he took office in 1982 and is frantically seeking a new direction. Some members blame Mr Scharping for the party's turmoil and would like to see him replaced. The media paints him as lacklustre, incapable and without charisma.
The Social Democrats came close to toppling Mr Kohl in last October's federal elections, but since then ideological cracks within the party have widened.