Turnout has been low on the first day of Poland's referendum on European Union membership, according to official figures.
Even Poland's former pro-Soviet leaders have been voting "yes"
Only 17.61% of registered voters cast ballots on Saturday, said the head of the electoral commission.
Polling stations will open again on Sunday morning for a second day of voting, with a 50% turnout needed to validate the poll.
Opinion polls have suggested most Poles support EU membership - but if the referendum is invalid, the issue will have to be decided in parliament.
One of the first to vote on Saturday was Prime Minister Leszek Miller who said this was "one of the biggest days in Polish history".
Casting his ballot, President Aleksander Kwasniewski predicted that more people would turn out on Sunday.
Former Communist leader Wojciech Jaruzelski, who imposed martial law in 1981, said he had voted yes.
"It's a new reality and you have to take it into account. I took
account of it by voting for Poland's entry into the EU," he said.
Two-thirds of voters are expected to cast a ballot and at least two-thirds are set to support EU membership, according to the latest opinion polls.
In the first few hours, correspondents described a slow stream of people voting.
In the capital, Warsaw, the authorities were offering free museum tickets to dissuade people from leaving the city during the weekend.
Prosperous city dwellers are among those keenest on EU membership, while poor farmers, market traders and the unemployed are most likely to be against it.
"Nothing will change for me if we join the EU but we will have to listen to orders from Brussels," no-voting farmer Jozef Knapik told Reuters news agency in the southern village of Cianowice.
His neighbour, Marian Molik disagreed: "I grow blackcurrants and much of it goes to Germany. I am in favour of the EU, because I'll be able to sell more blackcurrant there."
One "Yes" voter who raised a few eyebrows was Poland's Soviet-era military dictator, General Wojciech Jaruzelski.
"[Once] I would have said that [Polish EU entry] was science fiction, the theatre of the absurd," the 79-year-old former leader told reporters.
"It's a new reality and you have to take it into account. I took account of it by voting for Poland's entry into the EU."
Fewer than half of the voters took part in two previous referendums held in the 14 years since the end of communist government in Poland.
And in Hungary's referendum on EU membership on 12 April turnout reached only 45.6%.
If the referendum is declared invalid and the issue referred to parliament, a two-thirds majority will be required in both houses. This could be difficult to achieve in the lower house.
29 million voters
25,000 polling stations
Voters must be aged 18 or over
50% turnout threshold
Polls show more than two-thirds favour of membership
The BBC's Central and Eastern Europe analyst, Jan Repa, says this would involve some complicated inter-party trade-offs, including probably the resignation of Prime Minister Miller.
The failure of the referendum would also rock financial markets.
The Polish stock market, which has rallied by 10% since April, is anyway expected to inch down on Monday as investors engage in profit-taking.
Voting ends at 2000 (1800 GMT) on Sunday.
An exit poll will also be released on public television as soon as voting stations close. Initial results will be published on Sunday night.
The final result is expected at 2000 (1800 GMT) on Monday.