Among them are former managers like Mr. Senkut and Corey Cleek, a onetime senior manager of Internet marketing at eBay Inc. He recently left the San Jose, Calif., Internet auctioneer after working there for five years and profiting from his eBay stock options. The 34-year-old began putting money into start-ups in 2004. While he declines to specify how many start-ups he has bankrolled, he says he typically invests $25,000 to $100,000 in a company, particularly if the ventures are in Internet media and electronic-commerce.

Mr. Cleek still counts himself as a working stiff. Several months ago, he moved to Nashville, Tenn., to join a digital music start-up as its general manager. Every few weeks, he commutes back to Silicon Valley to check on his angel investments. "I make the time for angel investing because it's a passion," he says.

The re-emergence of angel investing may be a sign of froth in the tech market. During the dot-com boom, many individuals rushed to put money into start-ups just as tech stocks were nearing their zenith. When the bubble burst, many of these investors lost their shirts. "Angel investing is highly dangerous," says Naval Ravikant, a tech entrepreneur who lost money on some angel investments he made earlier this decade. "It's a game of poker" because so few investments typically succeed, he says. In general, angels say half of the start-ups they invest in likely will fail.

Today's angels say they are aware of such risks, but add that they expect one or two good deals to outweigh the bad ones. Gil Penchina, an eBay vice president, says his strategy is to invest in as many start-ups as possible. "I subscribe to the theory that you take as many bets as you can," says Mr. Penchina, 36. "Angels are looking for a return of 25 to 50 times what they put in, so if even one deal pays off, you're in good shape."