The pathogenesis of aminoglycoside nephrotoxicity is intimately related to the extent of drug accumulated in the renal cortex. In the framework of searching for preventive measures of aminoglycoside-induced nephrotoxicity, we investigated the influence of dosage regimen on the renal cortical accumulation of gentamicin and netilmicin in humans. Patients with a tumor partly involving one kidney, with normal renal function, and scheduled for nephrectomy received one dose of either gentamicin (4.5 mg/kg) or netilmicin (5 mg/kg) as a single short-term infusion or as 24-hour continuous infusion. Treatment started 24 hours before surgery. Serum aminoglycoside pharmacokinetics were examined during treatment and renal cortical tissue was sampled at the moment of operation for drug determination. The short-term infusion schedule yielded cortical concentrations of 103.2 +/- 36.3 and 137.4 +/- 34.6 micrograms/gm for gentamicin and netilmicin, respectively. Tissue levels after continuous infusion were 158.1 +/- 52.9 and 178.5 +/- 21.8 micrograms/gm for gentamicin and netilmicin, respectively. For each aminoglycoside, a single short-term infusion resulted in significantly lower renal drug levels than did a continuous infusion of the same dose. From the nephrotoxicity point of view, these data support the administration of gentamicin and netilmicin as once-daily injections. This also supports the appropriateness of further studies to determine clinical efficacy of once-a-day dosing for aminoglycosides.