Pityrosporum ovale is the yeast form of the dimorphic lipophilic fungus Malassezia furfur which is part of the normal skin microflora in adults. It is suggested that Pityrosporum ovale has a primary role in the pathogenesis of Dermatitis seborrhoides. The aim of the present study was to determine the titer of the common antibodies against superficial antigens of Pityrosporum ovale in the serum of Dermatitis seborrhoides patients and compare the results with the findings of examinations of serum antibodies in healthy subjects and patients with Pityriasis simplex capitis, Pityriasis versicolor, Pityrosporum folliculitis. Indirect immunofluorescent technique was used in the study. The Pityrosporum ovale antigen was obtained using own method. The results show that Dermatitis seborrhoides patients have an antibody titer of 1:640 and above, which is a higher titer than the antibody titers of healthy subjects and patients with other forms of the infection. The study results suggest that Pityrosporum ovale yeast might be implicated in causing a humoral immune response, which is important for the developing inflammatory reactions in Dermatitis seborrhoides. The results help to elucidate the pathogenic mechanisms and supplement the therapy strategy of the disorder. The authors are the first in Bulgaria to study the immune response to Pityrosporum ovale in healthy subjects and patients suffering from different forms of the infection.