A fatal case of lactic acidosis in a 84 year old diabetic woman taking buformin is reported. Buformin concentrations in serum, other body fluids and tissues were measured by gas chromatography. Serum buformin concentration at admission was 5.5 mg/l. Postmortem concentrations were: in serum 3.2 mg/l; in lung 2.8 mg/kg wet weight; in heart 3.0 mg/kg; in pericardial fluid 3.5 mg/l; in liver 5.2 mg/kg; in bile 6.3 mg/l; and in kidney 98 mg/kg.