Imipenem, a new carbapenem (thienamycin) beta lactam antibiotic which is clinically used in a 1:1 combination with cilastatin, an inhibitor or renal metabolism of imipenem, was evaluated in 25 patients; 11 children and 14 neonates. A mean daily dose of 60 mg/kg was given to children and the dose in neonates was 50 mg/kg. Clinically, 21 patients were cured, two failed to respond to treatment and two were not evaluable. Pharmacokinetic studies were performed in the 11 children and in 10 of the neonates. The mean elimination half-life of imipenem was 0.87 h in children and 2.1 h in neonates. The mean cilastatin elimination half-life was 0.73 h in children and 5.1 h in neonates. This difference in half-life between children and neonates is similar to the one noted between healthy adults and adults with renal insufficiency. No accumulation of imipenem was seen in neonates studied on the first and fifth days of treatment.