This double-blind randomized study was designed to compare the efficacy and safety of calcipotriol ointment (50 microg/g) with betamethasone dipropionate (64 mg/g) and salicylic acid (0.03 g/g) ointment in the treatment of nail bed psoriasis. Fifty-eight patients applied the given drug to the affected nails twice a day for 3-5 months, depending on clinical response. Efficacy was assessed monthly on the basis of nail thickness, measured in millimetres. Photographs of the treated nails were taken at baseline, and after 3 and 5 months. Tolerability was assessed at 3 and 5 months. In patients with fingernail psoriasis, after 3 months of treatment subungual hyperkeratosis was reduced from 2.3 +/- 0.1 mm (mean +/- SEM) to 1.5 +/- 0.1 mm (-26.5%) in the calcipotriol group and from 2.3 +/- 0.1 mm to 1.6 +/- 0.1 mm (-30.4%) in the betamethasone dipropionate and salicylic acid group [not significant (NS) between treatments, analysis of variance (ANOVA)]. After 5 months, responders showed a 49.2% reduction in hyperkeratosis in the calcipotriol group (from 2.8 +/- 0.1 mm to 1.4 +/- 0.2 mm) and 51.7% (from 2.1 +/- 0.1 mm to 1.0 +/- 0.1 mm) in the betamethasone dipropionate and salicylic acid group (P < 0.001 from baseline, NS between treatments, ANOVA). In patients with toenail psoriasis, after 3 months of treatment there was an overall reduction in hyperkeratosis from 2.6 +/- 0.1 mm to 2.1 +/- 0.1 mm (-20.1%) in the calcipotriol group and from 3.0 +/- 0.1 mm to 2.3 +/- 0.1 mm (-22. 9%) in the betamethasone dipropionate and salicylic acid group (P < 0.001 from baseline, NS between treatments, ANOVA). By the end of the fifth month there was a 40.7% reduction in hyperkeratosis in the calcipotriol group (from 2.1 +/- 0.1 mm to 1.2 +/- 0.1 mm) and 51.9% in the betamethasone dipropionate and salicylic acid group (from 2.7 +/- 0.1 mm to 1.3 +/- 0.1 mm; P < 0.0001 from baseline, NS between treatments, ANOVA). The results of the study show that calcipotriol is as effective as a combination of a topical steroid with salicylic acid in the treatment of nail psoriasis and represents a safe alternative in the topical treatment of nail psoriasis.