Fucolipid preparations isolated from individual small intestine mucosa from six CS A typed dogs were tested against various anti fucolipid antisera. The fucolipids from dogs with the CS A A antigen reacted exclusively with the anti A-like fucolipid antiserum. The fucolipids from dogs with the CSA Y antigen reacted exclusively with the anti Le-b-ike anti-sera. Likewise anti A-like fucolipid antiserum gave specific immunofluorescent reactions on colonic mucosa goblet cells of dogs with the CSA A antigen only, while the anti Leb-like fucolipid antisera gave positive reactions only on colonic mucosa goblet cells of dogs with the CSA Y antigen. The authors are indebted to Dr. Ray Hiramoto for the preparation of the fucolipid antisera and to Mr. David Law for valuable technical assistance. Supported by University of Alabama Medical Center Faculty Research Grants 82-6111 and 82-6117 and American Cancer Grant IN 66K. © 1974, SAGE Publications. All rights reserved.