A polypectomy was performed on a 68-year-old woman who had three gastric hyperplastic polyps. A focal signet ring cell carcinoma was discovered in one of the polyps, which was 2.2 cm in diameter and was located in the antrum. To study the carcinoma's phenotype expression, special mucin histochemical stainings were performed. The carcinoma infiltrated only into the mucosa. Intestinal metaplasia was scant. In the neoplasm neutral and foveolar mucin was predominant over acid mucin. The surrounding hyperplastic foveolar epithelium showed positivity for neutral mucin, and the intestinal metaplasia foci for acid mucin. This neoplasm has a mixed composition of mucins and shares histochemical characteristics with the surrounding hyperplastic foveolar epithelium.