A coagulation screen consisting of measurement of the prothrombin time, thrombin time, kaolin caphalin clotting time, platelet count, plasma fibrinogen level, fibrin degradation products and ethanol gelation test was performed on 24 patients with impairment of consciousness due to acute diabetic metabolic decompensation at the start of treatment and 24 hours later. 22 out of 24 patients showed at least one coagulation abnormality on admission of which the commonest were a prolonged prothrombin time, shortened kaolin cephalin clotting.time and raised plasma fibrinogen level. After 24 hours of treatment these values were more normal but 20 out of 22 patients still displayed some abnormality. 15 patients had two or more coagulation abnormalities on admission including 3 patients with haematological abnormalities suggestive of disseminated intravascular coagulation. This group was older and had higher blood ureas than those with fewer abnormalities, but plasma glucose, sodium, potassium and bicarbonate levels were similar in both groups of patients. All 5 patients with hyperosmolar non-ketotic coma and all 3 patients who died without recovering consciousness had two or more coagulation abnormalities on admission.