Beta-interferon-1a (betaINF-1a) is well tolerated at low dose (30 microg IM/week) in inclusion body myositis (IBM). The authors investigated the safety and tolerability of high-dose (60 microg IM/week) betaINF-1a in a randomized, placebo-controlled trial in IBM. Twenty-seven of the 30 subjects enrolled completed the study. The adverse event profile was similar for the placebo and betaINF-1a groups. betaINF-1a, at a dose of 60 microg IM/week, is well tolerated in IBM, but no differences in muscle strength or mass were observed between the placebo and betaINF-1a groups at 6 months in this pilot study.