Background: It has been proposed that Trichophyton infection is associated with atopy and allergy. Objectives: Our purpose was (1) to confirm whether atopy predisposes to chronic dermatophytosis and (2) to investigate whether Trichophyton infection induces atopic disease. Methods: Patients attending dermatology clinics and suspected of having dermatomycosis underwent in a prospective manner fungal culture and Trichophyton and inhalant skin tests, and blood serum was collected for total IgE and Trichophyton radioallergosorbent testing. Personal and family history of atopic diseases was also investigated. Results: According to mycologic culture, atopic history, and inhalant skin test results, patients were classified into 4 groups: (1) atopy plus mycosis (n = 28), (2) atopy (n = 26), (3) mycosis (n = 35), and (4) no atopy, no mycosis (n = 33). Patients with active mycosis (groups 1 and 3) demonstrated significantly increased positivity of Trichophyton skin tests compared with patients without fungal infection (groups 2 and 4), regardless of their atopic status, whereas atopic patients (those in groups 1 and 2) had significantly increased levels of total serum IgE compared with nonatopic subjects. Trichophytosis was not more prevalent in atopic than in nonatopic subjects, and atopic diseases were not more frequent in culture-positive than in culture-negative patients. Conclusions: Our results indicate that Trichophyton -specific IgE is observed in patients with trichophytosis regardless of atopy. (J Allergy Clin Immunol 2000;105:547-51.)