Two murine monoclonal antibodies MG7 and MGd-1 were used to label tissue specimens of gastric cancer and precancerous lesions with ABC method. The antigen to MG7 had a higher specificity to gastric cancer. The positive rate was 47.5% in early gastric cancer, 57.1% in advanced. But it was lower in precancerous lesions: 12.5% in dysplasia, 5% in intestinal metaplasia, 40% in adenoma. In addition, the stain was weaker than in gastric cancer. The antigen to MGd-1 had a higher positive rate in gastric cancer. It was 65.0% in early cancer, 88.6% in advanced. The positive rate was also high in precancerous lesions: 25.6% in intestinal metaplasia, 30.0% in adenoma, 57.5% in dysplasia. MG7 and MGd-1 did not react with the normal tissue and embryo gastric mucosa. Histologically, they show the strongest reaction to signet ring cell cancer.