Abstract
Two patients with rheumatoid arthritis developed pancytopenia during treatment with azathioprine 100 mg daily. In one patient this side effect occurred after three weeks, in the other after eight weeks of treatment. Rapid fall of platelets in one patient necessitated platelet transfusion. In the other patient additional treatment with allopurinol was probably responsible for the toxic effect. Haematological side effects of azathioprine are discussed.