Czech politicians are facing difficult coalition negotiations after the election created a parliament balanced equally between right and left.
Centre-right opposition leader Mirek Topolanek promised tax cuts
The Eurosceptic, conservative Civic Democrats led by Mirek Topolanek got the most votes but no overall majority.
President Vaclav Klaus asked him to start negotiations on forming a new government on Monday.
But a German-style "grand coalition" of right and left is unlikely, correspondents say.
The BBC's Rob Cameron in Prague says the political atmosphere is poisonous and Prime Minister Jiri Paroubek, leader of the Social Democrats, has said his party should now go into opposition.
They won 74 seats and their Communist allies took 26, giving them a combined total of 100, or exactly half the seats in the lower chamber.
The Social Democrats have dominated the government for the past eight years, steering the Czech Republic into the EU in 2004.
The opposition Civic Democrats won the largest share of the seats - 81.
Their centrist allies, the Christian Democrats and Greens, won 13 and six seats respectively in the 2-3 June election.
There were hopes the election would end four years of political instability, but the Czechs could be in for four more, our correspondent reports.