The correlation of the most important prognostic indicators was evaluated in 75 breast cancer cases. Estrogen-progesterone receptors and proliferating activity were analyzed by immunocytochemical methods (ER-ICA, PR-ICA, Ki-67). Both steroid receptors were inversely correlated with the proliferating activity (ER-ICA vs Ki-67, p less than 0.003; PR-ICA vs. Ki-67, p less than 0.0001). No correlation was found between steroid receptors or cell kinetics and tumor size or lymph node status. These findings confirm the relevance of biochemical and kinetic parameters as independent markers in breast cancer and suggest a routine use of the simple immunocytochemical methods in assessing the biological behavior of tumors.