The serum concentrations and safety of single daily dosing of amikacin were studied in 16 episodes of fever and granulocytopenia in children undergoing bone marrow transplantation. Amikacin (20 mg/kg) was administered as a 20 min iv infusion once daily for 7 to 19 days; all patients received concomitant therapy with ceftazidime. Peak amikacin concentrations measured immediately after infusion on day 1 and 4 of therapy averaged 72.29 +/- 11.6 mg/l and 74.02 +/- 19.29 mg/l respectively. A slight but statistically significant increase 30 minute post-infusion concentrations was observed in most patients during therapy. Serum amikacin were less than 3 mg/l in all trough samples and within 6 h post-infusion in most patients. A significant increase in serum creatinine was observed in one patient, who was also receiving cyclosporin A. Auditory function was evaluated in 10 patients and showed no changes. Although other drugs were added to cover Gram-positive or fungal pathogens, all patients survived. These data combined with the recent experience of single daily dose amikacin in adults supports further evaluation of novel dosage regimens of aminoglycosides in children.