Within the framework of previous investigations concerning the protective effect of estrogens during an experimental infection with Schistosoma mansoni in female hamster, the respective actions of the cis and trans forms of clomiphene have been studied. These two forms appear to be unable to assure a protective effect, the mean numbers of parasitic worms and the seric specific antibodies levels which have been observed in the treated animals do not significantly differ from those of the control group.