Measurements of peripheral blood flow using bolometry, thermography, ultrasonic Doppler index, and laser light scattering were made in nine patients with primary Raynaud's phenomenon before and after administration of 20 mg sublingual nifedipine and matching placebo. Following nifedipine treatment, there was some evidence of protection against reduction in blood flow, suggesting that this way of taking nifedipine is helpful. Self-administration of sublingual nifedipine before cold exposure may be an effective way of preventing the development of attacks of Raynaud's phenomenon in contrast with the conventional form of regular oral administration.