After a highly publicized battle with Napster and a longstanding refusal to sell its music via iTunes, Metallica has reversed course and made its songs available for individual, legal downloads on both sites.

"We think it's great that Metallica has come around and decided to embrace the legal digital distribution platform, and that music fans using Napster can now enjoy this vast and important catalog of music," says Matt Adell, vice president of Music Services at Napster.

"Over the last year or so, we have seen an ever-growing number of Metallica fans using online sites like iTunes to get their music," writes the band on its Web site, "So, in continuing with the tradition of offering our albums for sale online (which we've been doing for a few years through various sites), as well as making our live concerts available for download in their entirety, we are now offering fans the opportunity to obtain our songs individually."

On Tuesday the iTunes and Napster stores began to offer the band's entire back catalog of 10 albums — from its 1983 debut, "Kill 'Em All," to 2004's "Some Kind of Monster" — though only in the U.S. and Canada. (A post on Metallica's site reads, "Hopefully, this will get sorted out ASAP, but we didn't want our fans in North America to have to wait any longer while our overseas record company tries to get their s--t together!") To entice longtime fans to check out its digital stock, the group has added two previously unreleased live tracks on each of its first four albums.

So what took so long? Sometimes, explains Brian Garrity, Billboard magazine's business editor, "the biggest acts hold out until other artists test out the waters before them. Last year it was Madonna who made her catalog available on iTunes. Earlier this year it was the Red Hot Chili Peppers and the Dave Matthews Band."

From Metallica's perspective, the decision, says Garrity, boils down to simple economics: "Anyone who isn't participating in iTunes is leaving money on the table." And more revenue, of course, is music to anyone's ears.