Former Zambian President Frederick Chiluba has urged voters to back opposition leader Michael Sata in this month's presidential elections.
Michael Sata is seen as a strong candidate in this month's polls
Correspondents say the endorsement comes as a shock, even though Mr Chiluba has fallen out with the man he chose to become his successor.
President Levy Mwanawasa, who is seeking re-election, has ordered Mr Chiluba's prosecution for corruption.
A BBC correspondent says Mr Chiluba enjoys support, mostly in the north.
"I... declare my support for Michael Chilufya Sata [and] urge all of you in the country to vote for Sata. He is one of us, a humorous human being who easily mixes with people in their various social strata," Mr Chiluba said.
Mr Mwanawasa was elected in 2001, after Mr Chiluba failed to get the constitution changed to let him seek a third term in office.
President Mwanawasa suffered a mild stroke earlier this year but says he is fit enough to run for office.
The former president is accused of stealing $488,000 during the decade he was in power. He denies the charges.
Mr Chiluba's supporters say his prosecution is a political witch-hunt.
The third main contender in the 28 September poll is Lusaka businessman Hakainde Hichilema, who is backed by Zambia's founding father Kenneth Kaunda.