The possibility for patch testing procedures to detect contact allergy was examined in 85 hospitalized patients with forms of psoriasis. Exclusion criteria were active lesions on the back, the use of strong topical corticosteroids, methotrexate, cyclosporin and UV therapy. After screening, a group of 47 patients with different forms of psoriasis were selected for patch testing. Personal history, including topical treatment, occupation and domestic circumstances, were reasons to extend the standard series of allergens. Tars, nickel sulfate, perfume and balsam of Peru scored high. The overall positive rate was 68%. This is higher than that observed in earlier studies. The unexpected results are discussed in the light of the possible mechanism of action.