Pityrosporum orbiculare (pit.o.), the yeast form of Malassezia furfur, though usually considered to be a non-pathogenic saprophyte, in some individuals trigger various types of dermatitis. It is earlier shown that it is of importance in atopic dermatitis in the head-neck area in adults, and that elimination of the yeast by help of treatment with ketoconazole improve the dermatitis. In this large retrospective study of 741 patients prick-tested with an aqueous extract of pit.o., the occurrence of positive prick-test to pityrosporum was related to the patient's atopic manifestations. It was found that a positive prick-test to pityrosporum was related to active atopic dermatitis, and especially in the head-neck region. In contrast to the common allergens in the standard prick-test-series, however, pit.o. was not found to give positive prick-tests in patients with atopic conjunctivitis, rhinitis and/or asthma without active dermatitis. This finding strengthens the concept that hypersensitivity to the cutaneous microflora is of pathogenic importance in some cases of atopic dermatitis in adults.