The prehospital management of severe hypertension is limited by a paucity of pharmacologic agents suitable for field use. This prospective study was designed to test the safety and efficacy of intraoral nifedipine therapy in 50 patients with severe hypertension being transported by an urban emergency medical service system. Ten milligrams of nifedipine were administered. Serial blood pressure determinations were obtained at 3, 5, 10, and 15 minutes and patients were observed for possible side effects. A marked effect on systolic blood pressure (SP), diastolic blood pressure (DP), and mean arterial pressure (MAP) was evident and was statistically significant in all three categories by 3 minutes. MAP decreased from 169 to 129 mm Hg (delta MAP of 40 mm Hg) at 15 minutes with parallel changes in the SP (55 mm Hg) and delta DP (32 mm Hg). These changes were highly significant (P less than .01) when compared with those of 50 historical controls. No evidence of severe adverse effects were noted. Nifedipine appears to be a promising agent for the prehospital treatment of severe hypertension, but its proper role is not yet defined.