The opposition Socialist Party has won most votes in Bulgaria's elections - but not enough to form a government.
Sergei Stanishev says he is candidate for prime minister
The governing Liberal Party of former King Simeon Saxe-Coburg Gotha came second - followed by a party mainly representing the Turkish minority.
The Socialists need both runners-up to form a stable cabinet, says the BBC's Nick Thorpe in the capital, Sofia.
All the main parties have distanced themselves from the radical nationalist grouping - Attack - that came fourth.
Any new government faces negotiations over hopes for EU membership in 2007.
With almost all of the vote counted, the Socialists polled 31% of the vote, with the Liberals trailing on 20%.
The Movement for Freedom and Rights - largely representing ethnic Turks - took more than 11%, followed by the new radical Attack with 8%.
The negotiations which begin now will test relations within the parties as much as they test relations between them, our correspondent in Sofia says.
"We stand here as the winners of the most votes. I have long said that I am a candidate for prime minister and I am ready to take that responsibility," said the Socialist leader, Sergei Stanishev, after the party's win became clear.
If the Socialists fail to get both the outgoing Movement for Simeon II and the Movement for Rights and Freedoms, an alternative might be a centre-right government, says our correspondent.
This would include those two as well as three smaller centre-right formations.
In policy terms, whoever forms the next government will have little room for manoeuvre, our correspondent says.
Bulgaria has to meet strict criteria to be able to join the European Union in 18 months' time.
All the parties in the new parliament, with the exception of Attack, support those endeavours, says our correspondent.
Turnout was reportedly low, despite attempts to encourage people to vote - including a lottery.
Open to those casting ballots, this offered prizes include a car, TVs, DVD players and mobile phones.
The elections were the sixth since the fall of communism and return of democracy in 1990.
The Liberal government campaigned on Bulgaria's strong economy, while the Socialists promised to improve social welfare.