We examined immunological differences by non-specific and specific stimuli, using Trichosporon asahii (Ta), in 5 subjects in one family. The mother and her eldest daughter, among the 5 subjects in the family, were given diagnoses of summer-type hypersensitivity pneumonitis (HP) as a result of imaging, serological and histological examinations. The symptoms in both cases improved immediately after systemic corticosteroid therapy. Their home environment was cleaned up, and there has been no recurrence. All family subjects showed a positive reaction for the precipitin of Ta crude antigen, in addition four subjects, but not the father, revealed positive reactions for Type II Ta antigen in agglutination tests. In patients with HP, the concentrations of IFN-gamma by anti-CD3 + and anti-CD28 antibody stimulation were lower than those of healthy subjects. The concentrations of IFN-gamma and TNF-alpha for Ta antigen stimulation revealed no differences between the patients and healthy subjects in the family. In conclusion, we could not find any differences between the patients and non-patients in the family from the results of the serological and cytokine production measurement.