Venezuelans go to the polls with President Hugo Chavez facing what analysts are saying is the biggest electoral challenge yet to his socialist rule.
Henrique Capriles, a centrist state governor, edged toward the still popular Mr Chavez in final polls.
He ran a vigorous campaign which united the opposition and gave him a strong chance of ending Mr Chavez's 14-year rule.
Opposition sympathisers banged pots and pans in a protest against Mr Chavez last night, creating a racket in the upscale neighbourhoods of eastern Caracas.
In the city centre, which is more pro-government, the noise was drowned out by supporters playing his campaign music and shouting his name.
"I ask political actors from the left, right and centre to prepare emotionally to accept tomorrow's results. It is not going to be the end of the world for anyone," Mr Chavez said at a last-minute news conference at the presidential palace.
The 58-year-old president staged a remarkable comeback from cancer this year, but could not match the energy of past campaigns - or the pace set by his 40-year-old basketball-loving opponent.
Most well-known pollsters put Mr Chavez in front, but two have Mr Capriles just ahead, and his numbers have crept up in others.
There is a risk of violence if the result is contested.
There will be no formal international observers present for the poll, although Venezuela invited a delegation of the UNASUR group of South American nations to "accompany" the vote.
Local groups will be monitoring and both sides say they trust the electronic, fingerprint vote system. The opposition says it will have witnesses at all of the 13,810 polling centres.