One in every 20 U.S. Internet visits went to one of the top 20 social-networking Web sites in September, with MySpace the undisputed leader, a Web metrics firm said Wednesday.

MySpace, owned by News Corp., received 82 percent of visits to the 20 leading online gathering places, Hitwise said. From March to September, visits to the site rose 51 percent, outpacing the overall growth for the category of 34 percent.

Other social networking sites that received larger than average growth for the same time period were Bolt, 271 percent; Bebo, 95 percent; Orkut, 63 percent; and Gaia Online, 41 percent.

The influence of MySpace crossed over into other industries, as users who started with the site went elsewhere. In September, 2.4 percent of traffic to shopping and classifieds Web sites came directly from MySpace, an increase of 83 percent since March. Other industries that received increased traffic from MySpace were telecommunications, banks and financial institutions, and travel.

YouTube, the video-focused social networking site that search engine Google plans to acquire, saw a 249 percent increase in visits from March to September, HitWise said. The site ranked 26 among all U.S. Internet domains in September.