Voting has ended in the referendum on a change to the Egyptian constitution allowing presidential elections with more than a single candidate.
Some see the referendum as a first step towards democratisation
Government employees were taken by bus to vote at some polling stations, but there was only a trickle of voters at other stations, correspondents said.
Opposition parties including the banned Muslim Brotherhood urged a boycott, saying the changes are cosmetic.
Some activists who staged protests were attacked by governing party supporters.
The opposition says the proposed changes contain restrictions that ensure the ruling party retains power and are designed to deflect US pressure for more democracy.
The government says the conditions imposed by the amendment are needed to guarantee that only serious candidates run and those whose wealth would enable them to buy support are excluded.
President Hosni Mubarak, 77, is expected to stand for a fifth six-year term in office in September.
The government has been campaigning for a "Yes" vote in the referendum which it describes as historic.
The ruling NDP party has put up large banners in many streets in Cairo carrying slogans such as: "Yes to Mubarak, yes to freedom."
BBC correspondent Heba Saleh says an endless parade of government and NDP officials has gone on state television urging people to vote.
Prime Minister Ahmed Nazif said Egyptians would now become used to hearing a plurality of views and seeing more than one candidate.
At polling stations some voters expressed the hope it would be a first small step towards a more representative government.
"If I say no to change, then there will be no change. If people say no this time, then the chance will be missed," said marketing executive Hussein Farid.
But the opposition, who are largely barred from the state media, remain unconvinced, our correspondent says.
A group of about 50 opposition activists from the Kifaya movement - a coalition of activists from left-wing, nationalist and Islamist backgrounds - gathered in central Cairo after being prevented by police from holding a demonstration outside the high court.
Our correspondent says the security forces pinned them against a wall, while a much larger crowd of NDP supporters chanted slogans accusing them of being traitors.
NDP supporters set upon some opposition supporters
Activists who broke out of the security cordon were set upon and beaten up by the NDP supporters.
There were similar scenes on the stairs of the Journalists' Syndicate where Kifaya had called a press conference, but an estimated 150 NDP supporters armed with sticks broke through police lines and attacked them.
"It is the first time there is this amount of violence," said one Kifaya member.
"Even though we are a small group, we are not being allowed to voice our view."
She accused the security forces of allowing the NDP supporters to attack the demonstrators.
The movement says some 60 of its activists have been arrested.
The government has yet to announce turnout figures, but our correspondent says it will be hard to measure the impact of the boycott call.
The reason is that, with the exception of the Muslim Brotherhood, the main opposition parties do not have a much of a following.
Egyptian elections and referendums have always suffered from voter apathy bred by decades of authoritarian rule and rigged consultations.
The new rules require independent presidential candidates to have the backing of about 15% of members of parliament.
Established opposition parties that nominate candidates must have 5% of seats in both houses.