AbstractThe incidence of nephrotoxicity has been studied in 175 patients who received either gentamicin or tobramycin. All patients received individualized dosing regimens of the drugs based on pharmacokinetic parameters measured after the initial dose. Subsequent doses were calculated from the pharmacokinetic data to produce peak aminoglycoside levels of between 6 and 8 μg ml−1and trough levels that were below 2 μg ml−1. Renal toxicity was defined as a 30 per cent or greater increase in the serum creatinine level above the baseline value. Five of the 125 patients (4 per cent) who received gentamicin, and 1 of the 39 patients (2.6 per cent) who received tobramycin developed signs of nephrotoxicity. This difference was not statistically signif