AIM: To explore the role of the skin tissue from the host immunized with UV-attenuated schistosome cercariae against the challenge infection. METHODS: Eighty-eight mice were divided into four groups. Group 1 mice were challenged with 1 000±100 cercariae 5 wk after immunizing with 50±3 ultraviolet(UV)-attenuated cercariae of Schistosoma japonicum. Group 2 mice were challenged with 1 000±100 cercariae 5 wk after infecting with 50±3 cercariae. Group 3 mice were immunized alone with 1 000±100 cercariae. Local skin samples from mice of each group were taken at some certain time points from 6-120 h after infection or immunization for pathological observat ion. RESULTS: In Group 1, the cellular reactions against schistosomula in skin tissue were the most evident and persistant, in which the percent of eosinophils (EOS) was also the highest. Similar reactions were observed in Group 2 but not so intense as in Group 1. A large number of attenuated schistosomula prolonging their persistence in the subcutanous tissue until 120 h were observed in Group 3, but the number of schistosomula in the skin of Group 4 mice reduced evidently from 72 h, with slight cellular response. Ultrastructure studies revealed that most schistosomula in Group 1 were completely disintegrated around which were numerous EOS, lymphocytes and occasional degranulated mast cells. CONCLUSION: Cellular immune response in the skin of the mice immunized with UV-attenuated cercariae might play an important role in the protective immunity against challenge infection.