This study was undertaken in order to histochemically investigate the mucoid substances (acid mucopolysaccharide and sialic acid) in experimental and human pancreatic carcinoma. The degree of alcian blue staining in the ductal and interstitial portions of the pancreas increased, especially in hamster tubular adenocarcinoma which had been induced by N-nitrobis (2-hydroxypropyl) amine. The pancreatic carcinoma of the rats, induced by di-methyl benz (alpha) anthracene, was usually poorly differentiated carcinoma, in which alcian blue and toluidine blue staining was high in the interstitial portion when compared with that of the hamster pancreatic carcinoma, which was usually well differentiated. The rates of enzyme digestion of acid mucopolysaccharide and sialic acid showed more prominently in the rat pancreatic carcinoma than in the hamster pancreatic carcinoma. Mucoid substances in the ductal portion of human pancreatic carcinoma revealed properties similar to those of hamster pancreatic carcinoma whereas those in the interstitial portion were similar to those of rat pancreatic carcinoma. These results suggested that mucoid substances, especially acid mucopolysaccharide, both in experimental and human pancreatic carcinomas, may play an important role in tumor growth.