Abstract: AIM:Vaccination with radiation attenuated cercariae of schistosomes induced partial resistance in several hosts against challenge with normal cercariae.In the study,phenotype of lymphocytes in mice after vaccination with uv attenuated cercariae were investigated.METHOD:Female NMRI mice were used, each received either 200 untreated or 500 attenuated cercariae of S.japonicum or S.mansoni 6-7 mice of each group were killed at 3 d,5 d,7 d,10 d,14 d and 21 d after infection or vaccination.The axillary lymphnodes and the spleens were removed.Cells were prepared separately and were analysed by double colour immunofluorescence with conjugated monoclonal antibodies in a FACScan cytofluorimeter at 488 and 560 nm. RESULTS:Immunization with 500 attenuated cercariae was followed by a three to four fold increase in cell number in axillary lymph nodes,irrespective of schistosome species.In both cases,CD + 4 as well as B cell numbers increased,reaching peak levels at around 10 days;while CD + 8 cells did not appreciably vary over the three weeks of observation.CONCLUSION:On the basis of this study it is suspected that CD + 4 cells might play a significant role in the protective immunity elicited by uv attenuated cercarial vaccine.