We previously showed in a double-blind, placebo-controlled study that cyclosporin at a dose of 2.5 mg/kg per day is an effective treatment for palmoplantar pustulosis (PPP). In the present randomized, double-blind, placebo-controlled multicentre study we treated 58 PPP patients with placebo or cyclosporin at an initial dose of 1 mg/kg per day. Disease activity was calculated from the number of fresh pustules. Treatment success was defined as the number of fresh pustules not exceeding 50% of the patients' own baseline pustule number. In cases of treatment success the dose of the test medication was not increased and the treatment was kept blinded for a maximum of 12 months. Blinding was broken only on treatment failure of the initial test medication dose. The mean blinded treatment time was 5.1 months for the patients receiving cyclosporin and 2.1 months for placebo (P < 0.01). Treatment was kept blinded for 12 months for seven patients in the cyclosporin and two in the placebo group (P < 0.05). Patients whose treatment code was broken continued in an open dose-finding part of the study with dose adjustments of cyclosporin every second month. In cases of treatment failure the dose of cyclosporin was increased in steps of 1 mg/kg per day; in cases of treatment success the cyclosporin dose was decreased by 1 mg/kg per day. The minimum and maximum doses were 1 and 4 mg/kg per day, respectively. The mean effective dose during the dose-finding part was between 1.2 and 1.7 mg/kg per day. Two patients did not respond to the highest dose of 4 mg/kg per day. In two patients serum creatinine levels increased by > 30% of their own baseline. The other main adverse events were hypertension (seven patients) and hypertrichosis (six patients). After stopping cyclosporin treatment the mean number of fresh pustules showed a maximum after 2 weeks with a continuous decline after that. Twelve months after completing the treatment the mean number of pustules was reduced to 20.0 compared with 63.6 at baseline (P < 0.001); 11 patients were free from pustules and two of these were totally cleared. We conclude that cyclosporin at 1-2 mg/kg per day is an effective and well tolerated treatment for PPP in most patients.