The relationship between gentamicin pharmacokinetics and measures of bioelectrical impedance (BI) in elderly patients was investigated with the aim of developing a potential noninvasive means of individualising gentamicin dosage. Linear regression analyses identified height/resistance2 as a statistically significant predictor of gentamicin distribution volume, V, [adjusted (adj)r2 = 0.53, coefficient of variation (CV) = 15.2%], and resistance/reactance and creatinine clearance (CL(cr)) as predictors of total systemic clearance, CL, adj r2 = 0.52, CV = 20.1%. Individualisation of gentamicin dosage regimens based on these relationships to achieve steady- state (SS), peak gentamicin concentrations, C(ss,max), and SS trough concentrations, C(ss,min), of 7.0 and 1.0 μg/ml, respectively, in an independent group of elderly patients resulted in serum gentamicin levels of 5.9 ± 0.7 and 0.8 ± 0.4 μg/ml. Mean absolute prediction errors averaged 0.7 ± 0.5 μg/ml for C(ss,max) and 0.5 ± 0.3 μg/ml for C(ss,min). Measures of BI provided the best predictions of C(ss,max), whereas models based on CL(cr) alone were the best predictors of C(ss, min). This technique provides a means of complementing routine pharmacokinetic monitoring of gentamicin pharmacotherapy in the elderly hospitalised patient with reductions in patient discomfort and potential savings in time and cost.