A pharmacokinetic study was undertaken to determine the bioavailability of bumetanide in grossly oedematous patients. Six nephrotic patients were administered bumetanide 2mg orally (as tablets) and intravenously as single doses, in a randomised fashion. Serum bumetanide concentration-time profiles were characterised. Data were fitted to a 2-compartment model (5 patients) and a 3-compartment model (1 patient). Analysis of the areas under the curves showed a bioavailability of 0.84 ± 0.2, which is similar to that in normal individuals. It is suggested that the bioavailability of oral bumetanide in oedematous patients is not altered significantly and that the apparent resistance to diuretics in such patients may be due to another cause.