1 The pharmacokinetics of intravenously administered labetalol were studied in four patients with severe renal failure and in three normal subjects. 2 A new and sensitive method for the assay of plasma labetalol concentrations using high performance liquid chromatography is described. 3 Labetalol has a relatively large apparent volume of distribution (3.3-7.9 l/kg, two-compartment open model) and a relatively high plasma clearance (0.3-1.6 1 h-1 kg-1). 4 There were no significant differences between the patients with severe renal failure and the controls for any of the pharmacokinetic parameters measured. 5 In the presence of renal functional impairment, no modification of labetalol dosage is required. 6 In another study of 31 patients, glomerular filtration rate was measured at 3-month intervals for 3-18 months. In ten patients there was no change, in ten there was an improvement and in 11 there was deterioration, but in only three was this attributable to treatment. 7 In our experience with over 300 patients, we conclude that labetalol plus diuretic treatment is efficacious and safe in all grades of hypertension including those with all degrees of renal insufficiency.