Five patients with non-infected ascites were given 1 g cefotaxime 12 hourly for 8 days by i.m. injection. Serial blood and ascitic fluid specimens were assayed for cefotaxime. The mean half life of cefotaxime in the cirrhotic patients was almost twice as long as that described in normal human volunteers. The cefotaxime concentration in ascites varied between 2.1 and 17.6 mg/1.