We performed a meta-analysis of randomised clinical studies in which the efficacy and toxicity of the same total daily dose of aminoglycosides administered once-daily was compared with multiple divided daily dosing for treating human infections. Of twenty-eight publications identified from a literature search using Medline 19 publications of 20 study comparisons involving 2881 patients met the criteria for analysis. Netilmicin was investigated in 11 studies, amikacin in seven studies and gentamicin in two studies but no studies of tobramycin met the inclusion criteria. The meta-analysis showed that there was a small, statistically significant difference in clinical efficacy of 3.5% (95% confidence intervals 0.5% to 6.5%, P = 0.027) in favour of once-daily administration but no significant differences in bacteriological efficacy or nephrotoxicity were detected. Auditory and vestibular toxicity rates were low for all agents and no differences in these toxicities were identified between once-daily or multiple-dose administration regimens either clinically or by audiometry or electronystagmography. Aminoglycosides can be given once-daily without loss of efficacy or increased toxicity offering greater simplicity and potentially improved cost-effectiveness than can be achieved by giving these drugs in divided doses.