Proposition 29 would add a dollar per pack tax on cigarettes and use the money for cancer research.
The Secretary of State's Office shows the measure trailing by a 51 to 49 percent margin.
But Jim Knox with the American Cancer Society says it's still too close to call and supporters aren't giving up hope.
KNOX: "Our indications are that there are more than a million vote-by-mail and provisional ballots that remain uncounted so with only 65,000 separating us we're certainly not conceding anything at this point."
Proposition 29 opponents say they're encouraged by the lead, though they aren't declaring victory.
Polls showed a larger percentage of voters supporting the measure earlier this year.
But opponents - backed by the tobacco industry -far outspent supporters.