(FORTUNE Magazine) – Traditional news and entertainment companies like Time Warner (parent of FORTUNE's publisher), News Corp., and Disney have spent millions of dollars and made lots of noise about their involvement in interactive media. But so far they have little in the way of profits to show for it.

That's not so at Tribune Co., one of the few old-media companies making money in new media. And here's a twist: Tribune has struck gold not as an online publisher or programmer but as an investor.

The Chicago newspaper and broadcasting company made its first and best investment in 1991, when it paid $6 million for 10% of America Online, then a little-known, privately held online service. Those shares would now be worth nearly $300 million. Since then, Tribune has bought stakes in a dozen or so emerging media and technology companies, nearly all of which have turned into winning bets. The cumulative return of the $530 million Tribune New MediaVentures Portfolio has exceeded 50% on an annual basis since 1992.

Executives say their goal is to identify businesses that will help Tribune's TV and newspaper outlets extend their brands and develop online revenue sources. "It's vital to make these investments, not only to protect the franchises that we have but to create new ones," says Tribune CEO John W. Madigan. "It's proved to be a very effective way to get us into the new technologies."

Tribune's holdings include CheckFree Corp., the largest processor of electronic bill payments; Open Market, a software company that enables secure electronic commerce; Peapod, an online grocery-shopping service; and Excite, a leading Internet search engine. All have gone public since Tribune bought in. The company also owns stakes in startups like iVillage, an Internet publisher that runs such sites as InfoBeat, which delivers customized news and sports via E-mail.

Tribune is not a passive investor. Its executives typically get board seats and look for synergies with their investment partners. With AOL, for example, Tribune launched Digital Cities, a network of online city guides that has emerged as a leader in that crowded field. When Peapod needed to sell sponsorships to packaged-goods companies, the Chicago Tribune's ad-sales force lent a hand. Content generated by iVillage will soon be syndicated to newspapers by Tribune. "The thing that we've learned, maybe more than anything else, from these companies is how to think like entrepreneurs," said David Hiller, Tribune's senior VP for development.

Of course, not all the deals have paid off. Tribune lost money on a startup that it created to sell photos and graphics online, and an interactive TV-listings service formerly known as Starsight struggled before being absorbed by a competitor.

But Tribune's investment gains have more than covered the costs of launching its own media properties on the Net. Last year Tribune realized gains of $151 million, mostly by selling shares of AOL and CheckFree, while losing about $30 million from its internal online ventures. That may provide some comfort to rival media executives: For all its Net savvy, Tribune still can't make money online by itself.