Germany's most populous state of North Rhine-Westphalia has voted to end 39 years of rule by Chancellor Gerhard Schroeder's party, exit polls suggest.
Incumbent governor Peer Steinbrueck (left) looks set to go
The polls gave Mr Schroeder's Social Democrats (SPD) 37.5% of the vote - well behind conservatives with 45%.
If confirmed, this would be a big blow to the chancellor ahead of the general election planned for next autumn, says the BBC's Tristana Moore in Berlin.
The SPD chief, speaking after the exit poll, said the vote could be this year.
And the loss of North Rhine-Westphalia - a key stronghold - would also mean the end of the last coalition of Social Democrats and Greens at regional level.
Some 13 million people were eligible to vote in Germany's most industrialised state.
North Rhine-Westphalia includes the Ruhr Valley, known for its coal and steel production.
Its economy and population are bigger than many independent European countries, and its GDP is higher than that of Brazil or Russia.
But, of Germany's five million unemployed, more than one million live in North Rhine-Westphalia.
Schroeder's SPD has been haunted by the unemployment issue
For nearly four decades, the Social Democrats have ruled there, benefiting from the solid working-class electorate.
But the exit polls carried by state television channels ZDF and ARD showed the conservative Christian Democratic Union (CDU) comfortably ahead.
Our Berlin correspondent says these polls are usually reliable, and the result, if confirmed, will fuel speculation of a possible cabinet reshuffle in Germany.
Mr Schroeder may have to look again at controversial reforms - and the economy in general, our correspondent says.
Before the poll, Christian Democratic leader Angela Merkel, who is likely to challenge Mr Schroeder in the 2006 general election, said: "A success for us would be a decisive point for the whole of Germany."
The CDU have portrayed this region as an engine that will not start.