Italian Prime Minister Silvio Berlusconi's centre-right coalition has lost control of Milan and Naples in local elections.
The run-off polls are seen as a key test of Mr Berlusconi's popularity, as he faces multiple corruption trials and sex scandals.
Centre-left candidate Giuliano Pisapia won in Milan with about 55% of the vote over Mayor Letizia Moratti.
Milan, Mr Berlusconi's power base, has been run by conservatives for 18 years.
The city, Italy's financial capital, is Mr Berlusconi's birthplace and where he got his start in business and politics.
Some six million voters were eligible to cast their ballots in 90 towns and six provinces, but the results in Milan and Naples are seen as most important.
Ms Moratti got 45% of the vote in Milan.
In Naples, Luigi de Magistris of the Italy of Values party won 65% of the vote in a landslide victory over Mr Berlusconi's candidate, Gianni Lettieri.
Mr Lettieri had been seen as the favourite, but failed to win an outright majority in the first round of voting earlier in May.
'Hold our nerve'
Analysts say the loss in Milan could threaten the coalition of Mr Berlusconi's People of Freedom party (PDL) with the Northern League, which has become increasingly disenchanted with the prime minister.
"It's clear we have lost. The only thing to do is to hold our nerve and carry on," Mr Berlusconi told journalists with him on a trip to Romania.
He said he had spoken to Northern League leader Umberto Bossi, who told him the government would stand and carry on with plans to the government's budget deficit.
The prime minister said before the vote that to lose in Milan was "unthinkable" and called the city election a referendum on his leadership.
Campaigning became increasingly vicious before the vote, with Mr Berlusconi warning that Milan would be turned into "Gypsytown" if Ms Moratti was defeated.
Ms Moratti, a former minister for Mr Berlusconi, spent an average of US$400 (280 euros, £240) for every vote she obtained - 100 times more than her opponent.
Earlier in May, five TV stations - including several owned by Mr Berlusconi's Mediaset - were fined by Italian regulators for giving Mr Berlusconi more coverage than his opponents.
The elections are the first big test he has faced since the start of several corruption trials and scandals - including allegations of having had sex with an underage prostitute.