The expression of carbohydrate antigens specific to Span-1, CA 19.9, and SLEX in cancer tissues and nuclear DNA ploidy patterns were studied from tissue specimens of lesions excised from 137 patients with gastric cancer. The frequency of detection of each antigen was augmented with advanced invasion depth and progress in regional lymph node metastasis. In the cases which were positive for all three kinds of antigens, lymph node metastasis and lymphatic or venous invasion were detected with significantly higher frequencies than in the negative cases. The DNA histograms showed a DNA ploidy pattern of Type Ia or Ib in the cases negative for these antigens and a non-diploid or aneuploid pattern of Type II or III in many of the positive cases. These findings suggest that an immunohistological study of gastric cancer using monoclonal antibodies, combined with a nuclear DNA ploidy analysis, might be useful for understanding malignancy of the tumour.