Fifty-four neonates were included and completed the study. Twenty-seven neonates were given 2.0-2.5 mg/kg of gentamicin twice daily while 27 neonates were given 4.0-5.0 mg/kg of gentamicin once daily. The twice daily dose and the once daily dose group had mean steady state gentamicin peak concentrations of 5.94 +/- 1.57 mg/l and 8.92 +/- 1.59 mg/l, respectively (p<0.05) while their trough concentrations were 1.44 +/- 0.49 mg/l and 0.90 +/- 0.35 mg/l, respectively (p<0.05). There were 3 neonates (11.11%) in the twice daily dose group whose peak and trough level were not within the desirable therapeutic range, two patients with too high trough level (>2 mg/l) and one with subtherapeutic peak level (<4 mg/l). Only one patient in the once daily group had undesirable trough level that was higher than 1.5 mg/l but less than 2 mg/l. Treatment with a once daily dose did not present more nephrotoxity than a twice daily dose regimen and had the tendency to have less effect on renal function. Once daily dosage can achieve the equivalent efficacy compared to a twice-daily dosage regimen. All neonates in twice daily and once daily dosage groups showed improvement in clinical outcome. Therefore, a once daily dose of gentamicin with 4.0-5.0 mg/kg could be an appropriate regimen in term neonates during the first 7 days of life. This regimen produces peak concentration that may have greater clinical efficacy and trough concentration with less toxicity than conventional dosing regimen.