Twenty-six patients with idiopathic Raynaud's phenomenon participated in a double-blind, crossover clinical trial comparing the clinical effect of nifedipine with that of placebo. Four patients discontinued the study because of side effects and one patient defaulted at the return visit. Nifedipine significantly reduced frequency and severity of attacks (p < 0.01). In an overall evaluation of drug effectiveness, 19 of 21 patients preferred nifedipine to placebo (p < 0.01). Nifedipine proved to be effective in the treatment of idiopathic Raynaud's phenomenon, but side effects should be expected in some 30%.