Four monoclonal antibodies specific to various Lewisx-related antigens were tested for binding to monolayers and detergent extracts of the human colon carcinoma cell line HT-29 P and its metastatic variant HT-29 LMM. Only monoclonal antibody FH6 (antisialyl-dimeric Lex) bound more to the metastatic variant compared with HT-29 P. Detergent extracts of human tissues were then assayed for their FH6-binding activity. Normal colonic mucosa displayed less FH6 binding than either Dukes stage B or D primary colon carcinomas. Liver metastases from colorectal carcinoma demonstrated greater binding than stage B and stage D primary tumors, and more than normal liver. Expression of sialyl-dimeric Lex increases as the metastatic potential of colorectal carcinomas increases, and is related to the progression of colorectal cancer.