Carbohydrate antigens can be designed by referring to previously defined carbohydrate structures. We have generated a novel monoclonal antibody (MAb) (F1 alpha-75) against an artificially designed antigen (F1 alpha), using organic-synthetic chemistry methods and hybridoma technology. F1 alpha (Gal beta 1-->4GlcNAc beta 1-->6GalNAc alpha 1-->Ser/Thr) belongs to core type 6 of O-linked glycans, which has not been previously reported in human cancers. To produce antibodies against F1 alpha, a glycolipid was synthesized which carries the carbohydrate portion of F1 alpha on a ceramide foundation (Gal beta 1-->4GlcNAc beta 1-->6GalNAc alpha 1-->Cer). The MAbs we obtained (F1 alpha-75, F1 alpha-87) specifically recognized F1 alpha and had only a very weak or no cross-reactivity with other glycolipids similar to F1 alpha. We investigated the expression of F1 alpha in human tissues, including 110 gastric cancers, 73 colon cancers and 42 pancreatic cancers. F1 alpha was found in human cancerous tissues but not in normal adult tissues. The rate of positive staining with F1 alpha-75 was 80.0% for gastric cancer, 52.4% for pancreatic cancer and 38.4% for colon cancer. F1 alpha-75 also reacted with the tissues neighboring gastric and pancreatic tumors but not intensely. Among fetal tissues, F1 alpha-75 reacted with the pyloric glands of the stomach, the centro-acinar cells of the pancreas, the convoluted tubules of the kidney and the terminal bronchioles of the lung.