In order to further characterize and provide a possible mechanism for the asymmetrical involvement of forearm muscles in inclusion body myositis (IBM), we measured isometric hand and pinch grip strength, and forearm muscle girth on 15 IBM patients. Forearm muscle strength and girth were significantly greater on the dominant versus nondominant side: mean grip strength, 173.9 vs. 98.8 N; mean pinch strength, 47.6 vs. 29.7 N; and mean forearm girth, 22.5 vs. 19.9 cm. This observation may suggest a role for exercise in delaying the disease progression in IBM.