The latex of "Crown-of-Thorns" (Euphorbia milii var hislopii) is a potent plant molluscicide and a promising alternative to niclosamide (NCL), today`s mostly used molluscicidal compound. In addition to being an effective molluscicide, NCL also kills miracidia and cercariae, the two free living stages of Schistosoma trematodes. It is active against other helminths as well. Owing to its prominent cestocide activity NCL has been used in human and veterinary medicine as a drug of choice to treat several tapeworm infections. However, the effects of E. milii on helminths have not been studied so far. In this study we investigated the effects of E. milii latex on S. mansoni eggs, miracidia and cercariae. Data on the toxicity of NCL to these developmental stages of S. mansoni were also obtained for comparative purposes.