The hypothesis that the pharmacokinetics of amikacin are more predictable than those of gentamicin or tobramycin was studied. In a three-way crossover design 58 volunteers received 7.5 mg/kg amikacin by iv infusion and either 1.5 mg/kg or 1 mg/kg gentamicin and tobramycin. The mean half-life and mean serum concentration at 1 h for each drug was determined. No consistent significant difference was found between the pharmacokinetics of amikacin and the other two drugs.