A series for Nm23-protein immunodetection was investigated in human breast carcinomas. Frozen sections were processed by automated immunoperoxidase procedure, and immunoprecipitates in positive tumors were quantified by processing digitized microscopic images. Nm23 immunohistochemical expression in tumors was correlated with clinicopathological data and with intra-tumoral proteins also detected by automated and quantitative immunohistochemistry. A positive Nm23 immunoreaction was observed in 58% of tumors, within cell cytoplasm. Nm23 expression was independent of the patient's age, and of tumor size, type and grade, but an inverse relationship was observed between Nm23 expression and axillary-lymph-node metastasis. An inverse relationship was also observed between Nm23 and P-53, CD-31, cathepsin D, tenascin and P-gp immunohistochemical expressions. But Nm23 expression was independent of c-erb-B product, growth fraction (MIB1/Ki67), and immunohistochemical expression of hormone receptors/P-S2. The results suggest that the anti-metastatic nm23 gene may partly act upon the regulation of tumor-cell proliferation (correlation with P-53) and may have some effects on epithelial-cell/stroma interactions (regulation of extracellular-matrix protease and of angiogenesis) independently of hormone sensitivity.