A patient with chronic active hepatitis developed vomiting, dyspnoea, tachycardia, diarrhoea and diffuse pains. For several years she had been treated with azathioprine and for a few weeks before admission with phenformin for mild diabetes. Laboratory examination revealed acute disseminated intravascular coagulation and lactacidaemia. Despite intensive treatment the patient died a few hours after admission, the post-mortem examination revealing diffuse pulmonary haemorrhages. The present case report and those published in the literature suggest that phenformin should not be given to diabetics who also have renal or hepatic disease. In any case, if phenformin is given, it should be stopped if hepatic, renal, infectious or thrombotic complications occur. In these cases and those of sudden unexplained deterioration in diabetics, hospitalisation is essential and lactic acid levels should be determined and coagulation tests performed.