In an investigation of the clinical features of Japanese cedar pollinosis in Toyama Prefecture, Central Japan, an epidemiological study was carried out in 1991 by means of questionnaires. There were 1,720 female and 1,163 male patients, a total of 2,883 patients. In both female and male patients, the highest incidence was found in those in their thirties. The most frequent onset was 19th March 1991, when the maximum number of air-borne pollen was detected and also the highest temperature in March was recorded. The 236 patients in the children's group ranged in age from 5 to 15 years, and the number of male children was greater than that of female. The number of patients tended to increase only gradually up to the age of 11 years, and then rapidly from 12 to 15 years of age. The greatest number of patients developed symptoms at the age of 10 years. HD-RAST positivity was definitely higher in the children group than in the adult group. No significant association was found between the age of development of symptoms and HD-RAST positivity.