(CNN) -- A ballot initiative to ban gay marriage in California appears headed for a narrow defeat, exit polls showed.
Voters in California, Arizona and Florida weigh in on constitutional bans on same-sex marriage.
Proposition Eight, which would eliminate the right of same-sex couples to marry in California, was losing -- 53 percent to 47 percent, according to the polling. If it were to pass, it would overrule a state Supreme Court ruling in May legalizing same-sex unions.
However, similar measures succeeded in Arizona and Florida, where voters approved constitutional amendments recognizing marriage as a union between one man and one woman, CNN projected.
In Arizona, where a similar measure failed in 2006, Proposition 102 passed with 56 percent. Florida voters approved the amendment by a 62-38 percent margin.
Arizona, California and Florida were the only states to weigh constitutional amendments banning same-sex unions, down from 11 states in the 2004 election.
The projected results were just some of the hot-button issues in an election where ballot measures were dominated by social issues from abortion and affirmative action to suicide and animal rights.
As of 2:30 a.m. ET, CNN had projected results on most major initiatives, based on actual results and exit poll data from key areas.
Fifty-seven percent of voters in Arkansas supported a measure to prohibit unmarried sexual partners from adopting children or from serving as foster parents. The measure specifies that the prohibition applies to opposite-sex as well as same-sex couples.
Tuesday was a day of relief for supporters of reproductive rights. Voters in Colorado rejected a measure defining a person to "include any human being from the moment of fertilization," which would have applied to sections of the Colorado Constitution that protect "natural and essential rights of persons."
South Dakota rejected a proposal to prohibit abortions except in cases of rape or incest or where the mother's life or health is at risk. A similar measure that did not include exceptions for rape or the health of the mother was on the ballot in 2006, but voters rejected it 44 to 56 percent.
Voters in Michigan chose to amend the state constitution to permit human embryonic stem cell research with certain restrictions. The embryos, which must have been created for fertility treatment purposes, would have to have been discarded otherwise, and they may not be used more than 14 days after cell division has begun.
Results are still pending for California's Proposition 4, which requires physicians to provide parental notification to guardians of minors at least 48 hours before performing an abortion.iReport.com: Watch Prop 8 debate in Utah
The marijuana reform movement also won victories in two states. Michigan became the 13th state to legalize marijuana for medical purposes, with 64 percent of the vote. Voters in Massachusetts also approved an initiative to decriminalize penalties for possession of less than an ounce of marijuana.
Voters in Nebraska approved a measure prohibiting state governments from discriminating against or granting preferential treatment to people based on race, ethnicity, color, sex or national origin. Results on a similar measure in Colorado have not been announced.
In Washington, 58 percent of voters supported a citizen initiative to allow adults with six months or less to live to request lethal medication prescribed by a physician. A physician is not required to comply, but anyone participating "in good faith" with the request would not risk criminal prosecution.
Arizonans also supported a measure to overhaul state laws prohibiting the employment of illegal immigrants. Under Proposition 202, only employers who know that an employee does not have legal status would risk having their business licenses suspended or revoked.
Many states also weighed budget-related proposals with significant implications for the generation of state revenue.
In Massachusetts, voters rejected a measure to cut the state personal income tax rate in half for 2009 and eliminate the state personal income tax starting in 2010. A similar ballot measure in North Dakota also failed.
Voters in eight states considered proposals related to gambling and lotteries, including Maryland, where current law prohibits the operation of commercial slot machines. Voters approved a constitutional amendment to authorize the use of video lottery terminals, or slot machines, at certain locations in the state to fund public education.
Arkansas also approved a constitutional amendment to establish state lotteries to fund education, overturning a law set in 1874.
South Carolina voters supported an amendment to its constitution that changes the age of sexual consent from 14 to 16.
Animal rights advocates also won victories in two states. Massachusetts passed a measure to ban greyhound racing by 2010 and California approved an initiative to outlaw the confinement of pregnant pigs, calves raised for veal and egg-laying hens "in a manner that does not allow them to turn around freely."