The number of songs sold via Europe's biggest music download sites has increased tenfold over the past year.
Music fans are downloading a range of songs, not just chart hits
More than a million downloads have been sold via sites such as Freeserve, MSN and Mycokemusic from January-March - 10 times up on the same period in 2003.
OD2, the firm that provides the downloads, said OutKast's Hey Ya! was the most popular song in the UK.
It said it proved there was demand for a "decent, legal alternative to poor quality illegal peer-to-peer networks".
Music fans are downloading a wide range of songs, with the top 100 downloads accounting for just 11% of sales, the company said.
UK DOWNLOADS, JAN-MARCH 2004
1. OutKast - Hey Ya!
2. Black Eyed Peas - Shut Up
3. Kelis - Milkshake
4. Michelle McManus - All This Time
5. Peter Andre - Mysterious Girl
6. Dido - White Flag
7. George Michael - Amazing
8. Will Young - Leave Right Now
9. Fountains Of Wayne - Stacy's Mom
10. Keane - Somewhere Only We Know
This contrasts with CD single sales, where the top 100 CD singles account for 77% of total CD singles sales.
"This indicates that OD2's legal download sites are introducing music-lovers to all kinds of new types of music," said OD2 chief executive Charles Grimsdale.
Meanwhile, a report by researchers at Harvard and North Carolina Universities has suggested that swapping songs online has had no negative effect on music sales.
The report said high levels of file-swapping had an effect on CD sales that was "indistinguishable from zero".
The research, conducted over 17 weeks in 2002, blamed "a reduction in music variety" and "a consumer backlash" for declining sales.
But official music industry bodies have branded the study "skewed".
The study says illicit song-swapping accounts for a "tiny fraction" of a 20% dip in music sales over the last three years.
It also suggests that album purchases experienced a peak in the 1990s as music fans replaced their vinyl collections with CDs.
The International Federation for the Phonographic Industries (IFPI) has sharply rebutted the findings.
IFPI market research director Keith Jopling said the report's methodology was "flaky", basing its evidence on the busy last quarter of the year when the nature of music sales is changed due to Christmas.
"They establish no causality between file-sharers and music sales. The link they make is tenuous at best," he said.
"Concentrating on the last period of the year is a major flaw, and they fail on their final answer," said Mr Jopling.
The IFPI and sister organisations say they have carried out their own research, and they have concluded that downloaders are twice as likely as non-downloaders to buy less music.