The protein product of c-erbB-2 and ras oncogene has been examined for its prognostic potential in both node positive and node negative breast cancer. Using a western blot analysis, levels of these proteins were determined in 159 primary human breast tumor specimens. We examined relationships between gene expression and coexpression with other established markers of prognosis, as well as clinical outcome. Multivariate analysis showed that nodal involvement was the most powerful prognostic factor for predicting overall survival (< 0.000) and disease-free survival (p = 0.001), whereas c-erbB-2 expression was second only to nodal status for predicting overall survival in the whole series (p = 0.05). A separated stepwise analysis was conducted for node negative patients who did not receive any kind of adjuvant treatment and for node positive ones who underwent adjuvant chemo or hormonotherapy. c-erbB-2 expression independently predicted poor survival among node negative tumors (p = 0.001) and was associated with ras expression among node positive cases (p = 0.04). If adjuvant treatment is included in the model, coexpressing tumors are less responsive to Tamoxifen and CMF regimens than those with low levels of protein expression (p = 0.04). These results are potentially of clinical value in separating a subset of node positive breast cancer patients for more intense postsurgical treatment. Among node negative patients, the sole expression of c-erbB-2 enhanced levels, is more likely to retain a predictive value in relation to the response after conventional adjuvant treatment.