Bronchial hypersensitivity was investigated by astograph in 25 nasal allergy patients without clinical symptoms of asthma and 103 healthy people from 20 asthmatic families. The data were compared with those obtained from 36 asthmatics. Intradermal skin tests and HLA typing were also performed on the members of asthmatic families. Bronchial hypersensitivity was present at a much higher rate in nasal allergy patients than in healthy people. It was also demonstrated that bronchial hypersensitivity was present even in non-asthmatics from asthmatic families, and the incidence of bronchial hypersensitivity tended to increase when complicated by nasal allergy. Increased bronchial hypersensitivity was shown in people from asthmatic families with positive skin tests to mites and house dust. Bronchial hypersensitivity seemed to be related to HLA-haplotype in the same family. The results of antigen sensitization as measured by intradermal skin reaction test suggested that hereditary factors play some role in the development of bronchial hypersensitivity.