After spending years in American political lore as more myth than reality, the much ballyhooed phenomenon of the youth vote may have actually gained some believers this week.

Figures compiled by the Center for Information and Research on Civic Learning and Engagement, a nonpartisan research center, found that 43 percent of eligible voters under age 30 participated in Tuesday’s first-in-the-nation presidential primary in New Hampshire.

That’s a significant increase from voter participation rates of 18 percent and 28 percent in the 2004 and 2000 New Hampshire primaries.

The turnout helped Sen. John McCain make a comeback win the Republican primary, where he was the leading vote-getter in all age groups except those aged 65 and older.

And though he didn’t win the Democratic primary, the youth turnout also was a major part of the reason Sen. Barack Obama finished a close second to Sen. Hillary Clinton. Mr. Obama received 60 percent of the vote from those aged 18 to 24, while Ms. Clinton won only 22 percent of the vote in the college-aged group.