The intradermal test of this disease was performed by injecting 0.02 ml of the antigen into the middle third of the volar surface of the forearm; the reaction was judged after 15 minutes and a diameter of 9 mm or more in wheal and/or 20 mm or more in erythema were regarded as the positives. The following results are presented on this basis. (1) The percentages of the dermal reactors for the subgroup by age were shown in Table 1. Age was important in the sensitivity of the intradermal test with schistosome antigen; the percentage of positive reactors was significantly higher in the adult group compared with the younger three groups as Minor 1, 2 and 3. The rates of dermal reactors were reduced in the adult group from 40.5% in 1973 to 17.8% in 1976. Lowering the concentration of nitrogen to 10 micrograms per ml in the antigen showed a decrease of the sensitivity in the intradermal test in all age groups. (2) Sex was important in the sensitivity of the intradermal test and males had a higher positive rate than did females; there was a significant difference in the percentage of the positive reactors between the sexes in the same age groups in both West and East parts of the survey area (Table 2). (3) It was noted that the percentages of the dermal reactors were higher for those in the West part than those for the East part as shown in Tables 3 and 4 and Figures 1 to 5. There was a close correlation between the distribution pattern of the wheal diameter and the positive rate for the intradermal test in the same area; this was shown in Figure 6 and also evidenced by a shift to the right of the frequency distribution curves in Figure 9. (4) These results indicate that the intradermal test with schistosome antigen proved to be satisfactory for observing epidemiological status of this parasitic disease in the endemic areas. It was also suggested that such snail-control practices as cementing irrigation ditches and periodic application of molluscicide, and the mass-treatment of infected persons might be effective in reducing transmission among peoples over a considerable area in Yamanashi Prefecture.