The man in charge of Kenya's fight against corruption has resigned just days after the government was accused of "massive looting".
Githongo has spent years fighting corruption
Veteran anti-corruption campaigner John Githongo said he "was no longer able to continue serving the government" but did not give any further explanation.
President Mwai Kibaki was elected in 2002 on a pledge to clean up Kenya.
Shortly afterwards, he appointed Mr Githongo, a former head of the Kenyan branch of Transparency International.
He had spent years leading the campaign against the corruption under former President Daniel arap Moi.
He resigned as the first-ever permanent secretary in the office of the president in charge of governance and ethics.
Donors initially welcomed Mr Kibaki's efforts to stamp out corruption and restored aid, which had been cut off under Mr Moi.
But some diplomats estimate that Kenya has lost some $1bn in corruption over the past three years and are threatening to cut aid once more.
The UK High Commissioner to Kenya Sir Edward Clay, who made headlines last year for lambasting the government for not tacking corruption in high places, last week said he had underestimated the level of graft.
"We are not talking about minor corruption. We are talking about massive looting," he said.
A Transparency International survey of perceived corruption rated Kenya 122nd out of 133 countries in 2003.