Infection can be a trigger and an aggravating factor in psoriasis. Antibacterial and/or antifungal agents are commonly used in the treatment of intertriginous psoriasis, because it is believed that flexures in psoriasis are often colonized by Candida species and Staphylococcus aureus. Bacterial and fungal cultures were studied from 32 psoriatic patients with no topical treatment in the intertriginous areas, from 13 psoriatic patients treated with topical steroids and from 19 patients with no psoriasis or other affections of the skinfolds. Untreated psoriatic patients were colonized by S. aureus significantly more often than the control group but infection seemed to be unlikely. Candida was not found in any of the groups. It is proposed that intertriginous psoriasis be treated with topical steroids alone and that the routine use of antimycotic and antibacterial combinations should be avoided.