North Dartmouth, Mass.—America's largest companies have upped their use of Twitter strongly over the past year, with 60% of Fortune 500 companies actively tweeting, compared with 35% in 2009, according to new research from the University of Massachusetts at Dartmouth.

The 2010 version of “The Fortune 500 and Social Media: A Longitudinal Study of Blogging and Twitter Usage by America's Largest Companies” was conducted by Nora Ganim Barnes, director of UMass Darmouth's Center for Marketing Research. In addition to the increase in Twitter use, the report also found that 35% of Fortune 500 companies consistently responded with @replies or retweets within 72 hours.

The largest of the large companies are most active on Twitter. The study found that the first 200 companies on the list accounted for half the corporate Twitter accounts.

However, standard blog usage has not increased significantly over the past year. Fortune 500 companies with public-facing blogs totaled 116 (23%), compared with 108 (22%) in 2009 and 81 (16%) in 2008.