The effect of aging on the total body clearance, volume of distribution, and half-life of gentamicin was examined in 99 febrile patients with various degrees of renal function. In the 50 patients who were 18 to 64 years old, clearance of gentamicin was 79.0 +/- 27.0 mL/min (mean +/- standard deviation), creatinine clearance was 98.6 +/- 33.3 mL/min, volume of distribution was 0.242 +/- 0.077 L/kg, and half-life was 2.63 +/- 0.90 hours. In the 49 patients who were 65 to 90 years old, these values were 36.9 +/- 16.3 mL/min, 51.2 +/- 21.2 mL/min, 0.244 +/- 0.102 L/kg, and 5.80 +/- 4.13 hours. Significant differences were observed between the two groups for all parameters except volume of distribution. Linear regression revealed good correlations between the disposition characteristics (clearance and elimination-rate constant) of gentamicin and age as well as creatinine clearance. However, there was no apparent relationship between the ratio of gentamicin clearance to creatinine clearance and age (r = .0731). These findings suggest that the disposition of gentamicin is independent of age but dependent on renal function.