The objectives of the study were to determine whether concurrent treatment with calcipotriol (50 microg/g) and either clobetasone 17-butyrate cream (0.5 mg/g) (moderate potency) or betamethasone 17-valerate cream (1 mg/g) (potent) or placebo (vehicle of calcipotriol) was more effective and/or caused less skin irritation than calcipotriol cream (50 microg/g) used twice daily. It was a multicentre, double-blind, parallel group study. Patients applied calcipotriol cream in the morning and either vehicle (n = 174), calcipotriol (n = 174), clobetasone (n = 175) or betamethasone creams (n = 176) in the evening for up to 8 weeks. Adverse events led to withdrawal in 20 patients (2.9%). The mean percentage change in PASI (psoriasis area and severity index) was -40.6 in the calcipotriol/vehicle group, -48.3 in the calcipotriol/calcipotriol group, -53.7 in the calcipotriol/clobetasone 17-butyrate group and -57.5 in the calcipotriol/betamethasone 17-valerate group. A statistically significant difference was seen between the four treatment groups (P = 0.006) with calcipotriol/vehicle being less effective than the other treatments. A statistically significant difference in favour of calcipotriol/betamethasone 17-valerate was seen between the calcipotriol/calcipotriol group and the calcipotriol/betamethasone 17-valerate group. The majority of adverse events were skin irritations, which were reported for 31.2% of patients treated with calcipotriol/vehicle, 34.3% of patients treated with calcipotriol twice daily and 23.8% vs. 17.1% of patients treated with calcipotriol/clobetasone 17-butyrate and calcipotriol/betamethasone 17-valerate, respectively. Skin irritation was seen statistically significantly less frequently in patients treated with calcipotriol/ clobetasone 17-butyrate or calcipotriol/betamethasone 17-valerate (P = 0.001), whereas no difference was seen between the other groups. In conclusion, calcipotriol applied twice daily was as effective as calcipotriol/clobetasone 17-butyrate, but slightly less effective than calcipotriol/betamethasone 17-valerate. The incidence of skin irritation was less for patients using concurrent corticosteroids, whereas treatment with calcipotriol/vehicle did not reduce the incidence of skin irritation when compared with calcipotriol twice daily.