Many critically ill patients have increased extracellular fluid which might affect ceftazidime pharmacokinetics. We investigated the pharmacokinetics of ceftazidime in 15 adult intensive care patients receiving 2 g of ceftazidime intravenously three times a day. The ceftazidime mean (standard deviation) apparent volume of distribution and terminal-phase half-life were 56.91 (25.93) liters and 4.75 (1.85) h, respectively, significantly greater than values reported previously for healthy controls (P < 0.001). The mean ceftazidime clearance and area under the curve at steady state were not significantly different from those previously reported for controls. We conclude that ceftazidime pharmacokinetics in critically ill patients were altered by an increased volume of drug distribution and elevated elimination half-life.