Thirty-five cases of invasive breast carcinomas in formalin-fixed, paraffin-embedded tissue sections were examined and scored for estrogen receptor (ER) and progesterone receptor (PR) proteins, tumor vascularity as determined by factor VIII-associated antigen (factor VIII) immunostaining, and proliferative activity as determined by proliferating cell nuclear antigen (PCNA) immunoreactivity. There was a high correlation between the immunohistochemical (IHC) scores and biochemical values for both ER and PR (p< 0.001). The IHC analysis was able to detect more cases that were both ER and PR positive compared to the biochemical assay (58% vs. 48%). Comparison of tumor vascularity and PCNA IHC score revealed that carcinomas with greater neovascularization showed greater proliferative activity (p= 0.008). Carcinomas with higher PCNA scores and tumor vascularity were more likely to have metastasized to lymph nodes, but these associations were not statistically significant. These results indicate that markers with important prognostic significance such as ER and PR can be readily performed in routinely processed tissue sections, and that immunohistochemical analysis of tumor neovascularization and proliferation in routinely processed tissues may be useful in predicting the behavior of breast carcinomas.