Amplification of c-myc and c-erb beta-2 (HER-2/neu) proto-oncogenes were analyzed in breast cancer tissues obtained from 100 patients without lymph node involvement (N-). An amplification of the c-myc gene was detected in four cases and a c-erb beta-2 (HER-2/neu) amplification in eight cases. The frequency of these abnormalities were compared to classical prognostic parameters as well as to new biological prognostic markers (cellular cycle, cathepsin-D and pS2 protein). Most of altered tumors were associated to some classical poor prognostic factors such as: steroid receptor-negative tumors, poorly differentiated tumors, high histoprognostic grade and tumor cell density. In contrast, no relation was found with new biological parameters. The analyses of these data in relation to clinical evolution will be of interest to evaluate their prognostic value.