Voters in South Carolina joined voters in Virginia and Wisconsin in approving constitutional amendments banning gay marriage.
Results on similar referendums in five other states _ Arizona, Colorado, Idaho, South Dakota and Tennessee _ were pending as vote counting continued across the U.S.
In South Carolina, nearly four out of five voters supported the ban.
The state already has a law against same-sex marriages, but supporters said a constitutional amendment would prevent activist judges from possibly opening the door to gay unions. The amendment says "a marriage between one man and one woman is the only lawful domestic union that shall be valid or recognized."
Though similar anti-gay marriage amendments passed previously in all 20 states to consider them, gay-rights activists were nursing hopes that the streak might be broken this year.
Gay marriage amendments were among the options in 205 state ballot measures Tuesday as voters in 37 states addressed an array of the United States' most divisive social issues such as banning abortion, boosting minimum wages and tobacco taxes, and legalizing marijuana.
The referendums, know as ballot measures, are proposed state laws that must be approved or rejected directly by voters within states. They are often held in conjunction with general elections for practical reasons.
Tuesday's measures included a riveting contest in South Dakota, where voters chose whether to uphold or reject a toughest-in-the-nation law that would ban virtually all abortions.
Nationwide, activists on both sides of the abortion debate were on edge over the campaign. If the ban is upheld, abortion-rights supporters are likely to launch a legal challenge that could lead all the way to the U.S. Supreme Court.
Colorado voters had an extra option _ a measure that would grant domestic-partnership rights to same-sex couples.
Conservatives hoped the same-sex marriage bans might increase turnout for Republicans. Democrats looked for a boost from low-income voters turning out on behalf of measures to raise the state minimum wage in Arizona, Colorado, Missouri, Montana, Nevada and Ohio.
In Missouri, a proposed amendment allowing stem cell research was a factor in the crucial Senate race there; incumbent Republican Jim Talent opposed the measure, while Democratic challenger Claire McCaskill supported it _ and got national attention after releasing a controversial campaign advertisement featuring actor Michael J. Fox, who suffers from Parkinson's disease.
Missouri _ along with Arizona, South Dakota and California _ had a sharp increase in tobacco taxes on its ballot. In California alone, big tobacco companies spent more than $56 million (?43.9 million)fighting a tax increase that would boost the average price of a pack of cigarettes to $6.55 (?5.14).
Even more money _ a state record of $133 million (?104.27 million) _ was raised in the fight over California's Proposition 87, which would tax companies drilling for oil in the state. The proposal sought to raise $4 billion (?3.14 billion) to promote alternative fuels and energy-efficient vehicles.
Nevada and Colorado both offered measures _ trailing badly in the polls _ that would legalize possession of up to an ounce of marijuana by anyone 21 and older. A measure in Rhode Island would restore voting rights to felons on probation and parole.
Michigan voters decided whether to bar the state government from using race and gender to determine who gets into college, who gets hired and who receives contracts.
Elsewhere, land use was a hot issue, part of a backlash against a 2005 Supreme Court ruling allowing the city of New London, Connecticut, to buy up homes to make way for a private commercial development.
In Maine, Nebraska and Oregon, voters considered measures that would cap increases in state spending _ similar to a controversial measure approved in Colorado in 1992.
Arizona voters were deciding on the most ballot measures _ 19 _ including four arising from frustration over the influx of illegal immigrants. One measure would make English the state's official language. Another would expand the list of government benefits denied to illegal immigrants.
Another Arizona measure proposed a civics incentive: It would award $1 million (?0.78 million)to a randomly selected voter in each general election.