The authors attempted to estimate the relationship between three biological parameters (nuclear DNA content, PCNA (proliferating cell nuclear antigen)/cyclin, HER-2/neu oncoprotein) and lymph node metastasis. We evaluated 37 breast cancers which were less than 2 cm in maximum dimension. Quantitative analysis was performed using a CAS 200 Image Analysis System, after Feulgen staining and immunochemical staining using anti-PCNA/cyclin monoclonal antibody and anti-HER-2/neu oncoprotein polyclonal antibody. In lymph node-negative cases 20.0% were aneuploid, while in lymph node-positive cases 58.8% were aneuploid. A total of 20.0% lymph node-negative cases were in the high proliferation group, as opposed to 52.9% of lymph node-positive cases. This analysis revealed a significant relationship between cell proliferation and lymph node metastasis. Analysis of the expression of HER-2/neu oncoprotein revealed no significant relationship between overexpression of HER-2/neu oncoprotein and lymph node metastasis, but the expression of HER-2/neu oncoprotein was significantly related to a shorter relapse-free survival.