Twenty-five children with serious Gram-negative infections were treated in a prospective study with amikacin 20 mg/kg administered in a single daily dose as a 30 min iv infusion for 4 to 12 days. In nine cases the amikacin was combined with beta-lactam antibiotics. Escherichia coli were the most frequent bacteria isolated followed by K. pneumoniae, Providencia and Enterobacter spp. and Pseudomonas aeruginosa with MICs ranging from 1 to 16 mg/l. Mean (+/- S.D.) peak and trough concentrations of days 1 and 4 of therapy ranged from 49 +/- 13.5 to 53.6 +/- 13.4 mg/l and 6 + 1.4 to 7.7 +/- 4.1 mg/l respectively. All patients were clinically and bacteriologically cured. No significant adverse reactions were observed. The results suggest that administration of a single daily dose of 20 mg/kg amikacin should be considered practical and safe in children. Further studies are needed.