Human immune responses are heterogeneous and may involve antagonism between T helper (T_H) lymphocyte subsets and their cytokines. Atopy is characterized by immediate immunoglobulin E (IgE)-mediated hypersensitivity to agents such as dust mites and pollen, and it underlies the increasingly prevalent disorder asthma. Among Japanese schoolchildren, there was a strong inverse association between delayed hypersensitivity to Mycobacterium tuberculosis and atopy. Positive tuberculin responses predicted a lower incidence of asthma, lower serum IgE levels, and cytokine profiles biased toward T_H1 type. Exposure and response to M. tuberculosis may, by modification of immune profiles, inhibit atopic disorder.