German Defence Minister Karl-Theodor zu Guttenberg has resigned after accusations of plagiarism.
Mr Guttenburg was stripped last month of his doctoral title after he admitted his PhD dissertation was flawed.
He said: 'I thank the Chancellor [Angela Merkel] for her support. But I have reached the limits of my strength.'
Mr Guttenburg apologised to parliament last week after being accused of copying parts of the dissertation without correct attribution.
German media have found scores of copied passages in his dissertation. He said he made mistakes but not deliberately.
Ms Merkel had backed Mr Guttenberg and opposition leaders said she did not fire him over fears it would anger conservative voters ahead of regional elections.
