By Daniel Schweimler
BBC News, Buenos Aires
The right-wing businessman Mauricio Macri, has won the first round of Buenos Aires mayor's elections.
Mauricio Macri has a clear lead
But he won't reach the 50% of the vote needed to avoid a second round and on 24 June he'll battle it out with Daniel Filmus, backed by the government.
The poll comes just four months before presidential elections and gives an indication of how the government of President Nestor Kirchner is doing.
Buenos Aires dominates Argentina, so the battle has been hard-fought.
The city is enjoying an economic boom but the rapid growth is also bringing problems such as pollution and crime.
Mauricio Macri: 45.5%
Daniel Filmus: 24%
Jorge Telerman: 21%
20% of results counted
Mr Macri is best-known as the owner of Boca Juniors football club, while Daniel Filmus, who is strongly backed by President Kirchner, is the national education minister.
The incumbent mayor Jorge Telerman, who got the job last year by default when his boss was sacked, is out of the race, finishing in third place.
Buenos Aires is reaping the benefits of an economic boom, with tourism thriving, new building works and low unemployment.
But such rapid growth brings problems such as pollution, transport chaos and rising crime.
The new mayor will have plenty of work on his hands.