A 74-year-old-man (case 1) was admitted to our hospital because of dry cough, fever, and dyspnea on effort. His daughter-in-law, a 53-year-old-woman (case 2), was also admitted to our hospital on suspicion of hypersensitivity pneumonitis (HP). Their diagnoses of HP were established by radiological, serological, and histological examinations. It was necessary to differentiate between summer-type hypersensitivity pneumonitis (SHP) and bird breeder's lung due to their special environment. Several examinations, including immunological findings of BALF, returning-home provocation test, and antigen inhalation challenge test, enabled us to establish their diagnoses of SHP.