Eight cases of D-penicillamine (DP) induced myasthenia gravis (MG) are presented. Seven patients were being treated for rheumatoid arthritis (RA) and one for scleroderma. The mean duration of DP treatment until the myasthenic symptoms developed ranged from 2-8 months. The DP dose reached 500 mg daily. It was found that the clinical and immunological findings were almost similar to those of idiopathic MG, but were less severe. All patients had increased titers of acetylcholine receptor antibodies in their sera. Discontinuation of D-penicillamine resulted in the complete resolution of myasthenic symptoms after 2-6 months. One patient required ventilation, immunosuppressive therapy and plasma exchange. No association was found between DP related MG and the various autoantibodies tested. Immunogenetic analysis showed that three patients had HLA-DR1, two HLA-DR3, one HLA-DR4 and one HLA-DR5. In conclusion, the clinical presentation of DP-induced MG seems similar to idiopathic MG. DP-related MG is relatively benign, although it sometimes can cause life-threatening muscle weakness requiring aggressive therapy. The relatively small number of patients included in this study, however, does not permit any firm conclusions regarding the HLA associations of DP-related MG.