The concentration of ceftazidime in serum and urine was measured after 2 g i.v. in 10 healthy volunteers and 19 patients with various degrees of renal insufficiency. Elimination observed in normal volunteers can best be described by a two-compartment model. In renal insufficiency elimination of ceftazidime is markedly diminished, resulting in a larger area under the serum level curve (area under the curve; AUC). AUC and glomerular filtration rate (as well as AUC and plasma creatinine) can be brought into a mathematical relation. From these relations a dose reduction factor (DRF) can be derived. By means of this factor a dose can be calculated for each degree of renal impairment which causes the same AUC that would be anticipated in a subject with normal renal function. Dose recommendations in tabular form are presented. The urinary recovery decreases with impaired renal function; nevertheless therapeutical urine levels are observed down to dialysed patients.