Two patients with classical rheumatoid arthritis developed myopathy during treatment with penicillamine. In both patients, electromyography and muscle biopsies were indicative of polymyositis. In one patient, muscle enzymes were not examined at the appropriate time; in the other patient muscle enzymes were raised. This latter patient also had a rash and, in the dermal epidermal junction of pathological skin, granular deposits of immunoglobulin and complement were found. The myopathy subsided in both patients after withdrawal of penicillamine.