The purpose of this study is to evaluate whether once daily treatment for up to 8 weeks of calcipotriol 50 mcg/g plus betamethasone 0.5 mg/g (as dipropionate) gel is safe and more effective than betamethasone 0.5 mg/g (as dipropionate) in the gel vehicle, calcipotriol 50 mcg/g in the gel vehicle or the gel vehicle used alone in patients with scalp psoriasis.