Eight patients with non-Hodgkin's lymphoma who were in clinical remission but showed residual masses after therapy were examined with magnetic resonance imaging at 1.5 T at the end of therapy, with the sequences TR/TE:500/35,500/70,2000/35 and 2000/70. Residual masses were found in lymphoid areas (7), spleen (3) and kidney (1). In three patients, T2 showed high signal intensity. Disease progressed in the following 1-3 months and active lymphoma was histologically identified. In the other five patients, T2 showed a very low signal intensity. One of them had a distant relapse in lymphoid areas but the remaining four patients are asymptomatic after a mean follow-up time of 13 months, suggesting that the lymphoma is cured and the mass inactive. We conclude that magnetic resonance imaging seems to distinguish active from non-active residual masses after treatment of non-Hodgkin's lymphoma patients otherwise in clinical remission.