Xiphidiocercariae, aquatic larval stages of some trematodes are considered a potential instrument for biological control of mosquitoes. In this study we evaluated its natural occurrence in Campinas region and two places in Vale do Ribeira (Registro and Miracatu), São Paulo State. Snails were obtained from fresh water collections from September 1996 to February 1999. The species collected were Lymnaea columella, Physa marmorata, Biomphalaria tenagophila, Biomphalaria sp., Drepanotrema cimex, D. lucidum and Drepanotrema sp. Fasciola hepatica, xiphidiocercariae (Haematoloechidae) and echinostomatid cercariae were detected in the lymnaeids snails from Miracatu, SP. In the same locality were found planorbids snails parasitized by furcocercariae, echinostomatid cercariae and xiphidiocercariae. The xiphidiocercariae found in the planorbids were different from those obtained from lymnaeids. One Biomphalaria sp. infected with furcocercariae was found in Louveira, SP. In the ROSA place (Campinas, SP) an individual of Biomphalaria sp. and one of L. columella were found infected by the furcocercariae and echinostomatid cercariae, respectively. In the place UNI-I, in Campinas, one L. columella was infected by furcocercariae. Double infection in snails from Miracatu was also observed