An Alcian blue staining, perchloric acid-soluble, antigenic acidic mucosubstance (GOA) was purified from human gastric signet ring cell carcinoma with DEAE-cellulose chromatography, Seqhadex G-200 and preparative polycrylamide gel electrophoresis. Specific antisera were raised which reacted in indirect immunoenzyme histology with normal goblet cells of the small and large intestine and with goblet cells of intestinalized gastric mucosa. In surgical resection specimens of the stomach (n = 100) and of the colon (n = 19) 3 gastric signet ring cell carcinomas and 3 colonic colloidal adenocarcinomas stained for GOA, demonstrating an immunochemical relationship with normal intestinal goblet cells.