OBJECTIVE To compare the potentially toxic effects in fullterm neonates of amikacin administered once daily, versus amikacin administered twice daily. METHODS A controlled, randomized, prospective study in which one group of fullterm neonatal patients received amikacin 15 mg/kg per dose once daily (n = 20), and the other received amikacin 7.5 mg/kg per dose twice daily (n = 20). Impairment of renal glomerular function was defined as a decline of less than 50% of the expected physiological drop in serum creatinine over time. Brainstem auditory evoked potentials were also evaluated and amikacin blood levels taken. RESULTS Fifteen patients in the once-daily group and 12 patients in the twice-daily group demonstrated at least one period of renal function impairment while in hospital. This decreased to five of 16 and four of 16 patients during follow-up. These differences were not statistically significant. Brainstem auditory evoked potentials did not find signs of ototoxicity at any time. CONCLUSIONS In fullterm neonatal patients, once daily dosing of amikacin is no more toxic than the twice daily regimen.