From 1965 to 1987, 126 patients who had gastric cancer invading the muscularis propria (pm) were treated with curative resection in the Department of Surgery II, Kyushu University. We examined the correlation between the proliferating activity of the tumor by staining the tissue for proliferating cell nuclear antigen (PCNA) and the occurrence of lymph node metastasis present in 46.8% (59/126) of the patients. Undifferentiated carcinoma was more frequent in these patients and lymphatic and vascular involvement was prominent. Patients with a lymph node metastasis had a higher level of PCNA staining in the tumors than did those without lymph node metastasis (labeling index: 36.5 +/- 9.6% vs. 25.3 +/- 8.3%) (P < 0.01). The survival rate for patients with lymph node metastasis was lower than that for those without this metastasis (P < 0.01). The 10-year survival rate was 63.6% for the patients with lymph node metastasis and 86.8% for those without lymph node metastasis. Thus, the presence of lymph node metastasis is associated with a high growth potential of tumor cells in pm gastric cancer. Close follow-up and adjuvant chemotherapy in the postoperative period is recommended for these patients.