US internet traffic to radio, gambling, retail and healthcare sites soared during March, according to statistics from comScore.

'March Madness', otherwise known as the NCAA basketball tournament, attracted a flurry of activity, prompting a 14 per cent gain in the online gambling category amid increasing political turmoil over internet gambling.

Sportingbet increased its traffic by 35 per cent to 975,000 visitors, while Upickem.net jumped 174 per cent to 396,000 visitors and SportsBetting.com rose 114 per cent to 145,000 visitors.

Radio sites saw a 27 per cent surge in visits in March to 61.8 million visitors, making it the top-gaining category for the month.

AOL Music led the way with 21.9 million visitors (up five per cent), followed by Yahoo Music with nearly 20.8 million visitors (up four per cent) and Clear Channel Online with 11 million visitors (up two per cent).

Other significant increases were experienced by Pandora.com (up nine per cent), Citadel Broadcasting Corporation (up 11 per cent) and Disney Music (up 17 per cent).

Healthcare sites experienced a 12 per cent increase in March to 26.3 million visitors. Walgreen Co led the category with 5.4 million visitors (up 10 per cent).

Drugstore.com captured the second position with 3.7 million visitors, followed by CVS with nearly three million visitors.

"American sports featured prominently in the top-gaining categories and properties in March," said Jack Flanagan, executive vice president of comScore Media Metrix.

"The NCAA tournament drove substantial traffic to online gambling sites during the month, while the start of spring training made MLB.com one of the top gaining properties.

"Both events also contributed to ESPN.com's surge in the top properties rankings."