The pharmacokinetic behavior of cimetidine has not been described in children, and there is no authoritative guideline on cimetidine dosage for children. Cimetidine pharmacokinetics were studied after a single intravenous dose and during three, incremental rates of continuous infusion in critically ill children. The mean elimination half-life of cimetidine was 1.44 +/- 0.41 hours. Compared to adults, these children had a relatively faster clearance (14.21 +/- 2.85 ml/min/kg) of cimetidine and a larger apparent distribution volume (2.13 +/- 0.63 l/kg). Based on our results, it appears rational to initiate cimetidine at a daily dose of 24 mg/kg in critically ill children.