Isradipine is a new potent calcium-channel blocking agent with highly selective action on peripheral vessels. In this single-blind study, its dose-related effect on cold-induced changes in finger systolic pressure (FSP) was investigated in ten female patients with primary Raynaud's phenomenon, and the side effects of isradipine treatment were evaluated. The patients were studied during 9 weeks of treatment. After 3 weeks of placebo, isradipine was given in doses of 1.25 mg b.i.d. and 2.5 mg b.i.d. for 3 weeks each. FSP was measured on local finger cooling to 10 degrees C. FSP at 10 degrees C expressed in percent of the value of 30 degrees C increased from 21 +/- 16% (M +/- SD) after placebo to 42 +/- 28% (p less than 0.05) and 62 +/- 25% (p less than 0.001) after treatment with isradipine 1.25 mg and 2.5 mg b.i.d., respectively. The subjective efficacy of the treatment was assessed with a visual analogue scale (VAS). The VAS rating increased from 17 (range 0-66) after placebo to 39 (range 12-88) (NS) and 68 (range 25-99) (p less than 0.001) after isradipine treatment with 1.25 mg and 2.5 mg b.i.d., respectively. Adverse effects of isradipine therapy were few and did not differ from those reported after the placebo period. This single-blind, dose-response study showed that isradipine in doses of 1.25 mg and 2.5 mg b.i.d. had favorable objective and subjective effects in patients with primary Raynaud's phenomenon and had no serious side effects.