A 27-year-old white woman received a renal allograft, following which immunosuppressive treatment was started. The transplanted organ functioned well. Sixteen months after transplantation she showed abnormal levels of serum glutamic oxaloacetic transaminase. Six months later frank jaundice developed. The clinical course, pathological findings, and laboratory data were compatible with drug toxicity in the liver and azathioprine appeared to be implicated. The patient died of hepatic failure.