Eight patients were treated with ceftazidime, four of whom had impaired renal function with creatinine clearances below 60 ml/min per 1.73 m2. The levels of ceftazidime in serum and extracellular fluid were determined. Half-life in serum and extracellular fluid was 2.5 and 2.2 h respectively for patients with normal renal function. For patients with impaired renal function the half-life of the drug was 7.9 and 115 h, respectively. The penetration of ceftazidime into extracellular fluid was around 50% in both groups. The levels achieved in both serum and extracellular fluid were satisfactorily high and prolonged, suggesting that a dosage regimen of 1 g twice daily is satisfactory.