Diazoxide was administered to sixteen pediatric patients (ages 10 months to 13 years) with secondary forms of hypertension. Admission BP was 178+/-8/130+/-5 mm Hg (mean +/- SEM). Diazoxide was administered rapidly intravenously in doses ranging from 2 to 7.5 mg/kg. A significant (P less than 0.001), linear log dose-response relation was obtained which showed that a 3 mg/kg dose of diazoxide lowered diastolic BP by an average of 30 mm Hg. In five patients reduction of idastolic BP by a single injection of diazoxide was no different than when the same total dose was given as two or three small injections repeated at fifteen to twenty minute intervals. It is concluded that 1) many hypertensive children respons significantly to doses of diazoxide smaller than the usually recommended 5 mg/kg; 2) diazoxide has a significant dose-response relation in hypertensive pediatric patients; and 3) the desired blood pressure response in hypertensive children can be titrated using repeated small injections of diazoxide.