To evaluate the relation between immediate hypersensitivity and environmental factors, a total of 2,187 allergic children were given the intracutaneous skin tests (IC test) and specific IgE antibodies (RAST) at Kudanzaka Hospital over a period of 21 years (1967-1987). The incidence of positive IC test to house dust (HD) and Japanese cedar pollen (sugi) increased, and that to molds increased transiently in the period 1965-1975. There was no sex difference in the incidence. Asthmatic children with allergic rhinitis scored higher both in IC test and RAST than those with asthma only. The more severely asthmatic children had a higher incidence of positive IC test to HD, molds, sugi, ragweed, cat dander, silk and buckwheat (sobagara). The recent rise of in the number of allergic diseases was partly proved by higher positive IC tests to HD and sugi. The number of positive test to HD mites also increased because twice as many non-wooden houses as wooden houses, have been built since 1969, and there were 3 times as many, high-rise building in 1975 as in 1965. Pollution and the increasing area of sugi forests were also responsible for increased allergic problems.