The effectiveness of repeated intravenous injections of labetalol in reducing blood pressure (BP) was evaluated in patients with severe hypertension. The subjects were 10 patients who were 29 to 61 yr old and who had diastolic blood pressure (DBP) of 125 mm Hg or higher. Repeated injections titrated from 20 to 80 mg were given at 15-min intervals until there was a reduction in DBP of 30 mm Hg or until 300 mg had been administered. The average reduction of BP ranged from 201 +/- 5/132 +/- 1 to 157 +/- 6/108 +/- 4 mm Hg (mean +/- SEM). Four patients responded with a reduction in DBP of 30 mm Hg or more with total doses of 60 to 220 mg. Of the remaining six who received the full dose, in four there was a 20 to 29 mm Hg reduction in DBP, in one there was a 10 mm Hg fall, and in one there was no reduction. There was a positive correlation between age and response to intravenous labetalol. No severe side effects were encountered. Intravenous labetalol is useful and well tolerated in patients with severe hypertension.