1 The pharmacokinetics of labetalol were studied in twelve hypertensive patients, ten of whom were not receiving other therapy. 2 Following intravenous administration there was a three- to fourfold variation in terminal elimination half-life, volume of distribution and total plasma clearance. The mean elimination half-life was 3.25 hours. 3 Following oral administration the drug was absorbed rapidly. Systemic availability varied from 11-86% (mean 33%). 4 Plasma levels correlated poorly with the acute effect on BP, raising the possibility of labetalol acting in a deep tissue compartment or alternatively an active metabolite contributing to its effect.