The pharmacokinetics of ceftazidime were investigated in eight normal subjects and eight patients with ascites after intravenous administration of 1 g of the drug. Samples of blood and ascitic fluid were collected for 6 h after dosage, and urine samples were collected for 24 h. Pharmacokinetic data were calculated by using a one-compartment model. The apparent volume of distribution and half-life of elimination (t1/2 beta) in patients with ascites were approximately three times those in normal subjects. In contrast, renal clearance was greater in the normal subjects. With respect to ascites, the mean area under the concentration-time curve was 95.3 +/- 38.3 micrograms X h/ml. The mean ratio of the area under the concentration-time curve for ascitic fluid to that for plasma was 69.9% (+/- 38.2). These data show that ceftazidime rapidly diffuses into the peritoneal space, in which concentrations greater than 10 micrograms/ml were present for at least 6 h.