The treatment of chronic graft-versus-host disease (GVHD) may present a difficult therapeutic problem. We used thalidomide to treat six patients with severe chronic GVHD who failed to respond to standard immunosuppressive agents. Four of the six patients showed a clear response to thalidomide, with the fifth patient showing a partial response. The best results were seen in patients with chronic cutaneous GVHD. Two of the patients developed neurophysiological evidence of a peripheral neuropathy, associated with clinical signs in one patient. Measurement of thalidomide plasma levels and pharmacokinetic curves showed a significant inter-patient variation. Peak plasma levels varied from 0.47 to 1.46 micrograms/ml. Thalidomide has a role to play in the management of chronic GVHD and further studies are needed.