The distribution of beta- and gamma-cytoplasmic actins was compared in the normal cells and dysplastic malignant breast epithelial cells. In the normal luminal epithelium, beta- and gamma-cytoplasmic actins were located in different cell compartments: gamma-actin was more expressed in the apical parts of epithelial cells while beta-actin was in their basolateral domain. Polarized distribution of actinic isoforms was partially preserved in the papillomas and fibroadenomas; a more pronounced coexpression of isoforms was detected in the dysplastic proliferates. In ductal and lobular in situ carcinoma cells, gamma-actin filamentous structures were absent while the gamma-cytoplasmic actin network throughout the cytoplasm was increased. It is generally accepted that the enhanced motility of cancer cells as to the nonmalignant situation is crucial in the process of cancer invasion. The authors' findings suggest that specific monoclonal antibodies to beta- and gamma-cytoplasmic actins may be used as supplementary markers that can differentiate benign and malignant breast neoplasms.