An attempt has been made to induce immunoprotection against cercarial infection through inoculation of live worms into the peritoneal cavity of mice. Although the worms were able to survive normally under these conditions, and no egg-laying could be detected, immunoprotection was obtained. Likewise, the inoculation of viable eggs, by circulatory and peritoneal routes, did not provide immunoprotection in mice with worms in the peritoneal cavity.