The susceptibility of B.alexandrina snails exposed to sublethal doses of copper sulphate or Bayer 73 was generally higher in infected snails than in non- infected one .This was specially increased as sporocyst development progressed to maturity Also, the prepatent periods of infected were higher in infected snails treated with either moulluscicides than in non infected groups. On the other hand ,coppersulphate decreased the infection rate of the snail more than Bayer 73