Diazoxide is given by rapid intravenous injection for the urgent reduction of high blood pressure in patients with all grades of renal function. Oral diazoxide produces less consistent effects. Protein binding of diazoxide is reduced in renal failure and this can be related to reduction of albumin concentration. There is a relation between impairment of renal function and the hypotensive effect of rapidly injected diazoxide. This is explicable in terms of the greater concentration of free (unbound) drug achieved after rapid injection in patients with renal failure. Renal clearance of diazoxide and its metabolites is impaired in renal failure but this is unlikely to affect its activity.