The efficacy of nifedipine and prazosin in the treatment of Raynaud's phenomenon was assessed in a prospective double-blind randomized cross-over trial in 15 patients. Each patient received one week of nifedipine 20 mg TID, one week of prazosin 1 mg TID, and 2 weeks of placebo. Nifedipine was shown to be effective in reducing both the frequency and the severity of Raynaud's phenomenon, whereas prazosin was ineffective. Before initiation of therapy in the 15 patients, pressor responses to the intravenous alpha 1-agonist phenylephrine were assessed in the basal state, 30 min after 20 mg oral nifedipine, and 30 min after 1 mg oral prazosin; the shift to the right of the log dose-vasopressor response curves to phenylephrine was similar with nifedipine and prazosin.