Voters in California have rejected a ballot proposition that would have made it the first US state to legalise marijuana for personal use.
With one-fifth of precincts counted, projections by CNN suggested 56% had voted against Proposition 19.
Adults would have been able to possess up to 28g (1oz) of cannabis, and local authorities would also have been able to permit commercial growing.
The legalisation would have put the state at odds with federal drug laws.
Proposition 19 was the highest-profile of the 160 ballot measures being decided in 37 states in Tuesday's mid-term elections.
Other measures dealt with abortion, tax cuts and health care reform.
Growing and selling marijuana for medicinal purposes has been legal in California since a similar vote in 1996. Since then, 14 other states and Washington DC have followed suit.
Supporters of Proposition 19 had argued that ending the prosecution of people with small quantities of cannabis would have freed up police to tackle violent crime and helped combat powerful drug cartels.
They also argued that it would have allowed the state to regulate the cultivation and distribution of the drug, and profit from its taxation. A recent report estimated California's crop to be worth about $14bn (£8.7bn).
But opponents - including every major newspaper, both the Democratic and Republican parties, and the two leading candidates for state governor - said it was a badly-written law that would cause chaos.
And last month, US Attorney General Eric Holder warned he would "vigorously enforce" federal drug laws if Proposition 19 passed.
After the first results of Tuesday's ballot came in, Richard Lee, a leading proponent of Proposition 19, said: "The fact that millions of Californians voted to legalise marijuana is a tremendous victory."
"We have broken the glass ceiling. Proposition 19 has changed the terms of the debate and that was a major strategic goal."
"With limited resources this time around we were able to build an enormously powerful coalition.... This coalition will only continue to grow in size and strength as we prepare for 2012."
In other ballot measures on Tuesday, voters in Massachusetts rejected a chance to lower the state sales tax from 6.25% to 3%.
Oklahomans meanwhile supported making English their state's "common and unifying language", requiring that people have a government-issued photo ID in order to vote, and prohibiting state courts from considering international law or Islamic law when deciding cases.
In Washington state, voters rejected a proposal by Bill Gates's father to bring in personal income tax for those earning over $200,000 (£125,000). Microsoft chief executive Steve Ballmer was a leading opponent.