C-erbB-2 DNA amplification and mRNA expression were analyzed by dot and Southern blots in 65 human primary breast tumors. Gene amplification was observed in 21 of 65 (32.3%) and elevated levels of c-erbB-2 transcript in 14 of 60 (23.3%) of the tumors analyzed. Only 55% of the tumors with c-erbB-2 gene amplification presented gene overexpression, showing an incomplete correlation between gene amplification and overexpression. No statistically significant correlation was observed between c-erbB-2 genetic alterations and other prognostic factors in breast cancer. However, patients with tumors presenting c-erbB-2 gene amplification and/or overexpression appeared to have a shorter disease-free interval than patients without c-erbB-2 genetic alterations. High levels of c-erbB-2 gene amplification were more powerful predictors of risk of recurrence than was overexpression of the gene. Cox univariate-bivariate analyses suggested that gene amplification was independent of nodal status to predict recurrence in breast cancer.