Fifty patients with typical infiltrating ductal adenocarcinoma of the breast were studied for amplification of the c-erb B-2 (neu/HER-2) oncogene within the tumor DNA. Amplification, ranging from 4 to greater than 50 copies per cell, was observed in 17 (34%) of the samples. The presence of c-erb B-2 gene amplification was not significantly correlated with patient survival, metastases, recurrence, or overall histologic grade. However, amplification was significantly associated with increased mitotic activity. Also, amplification of c-erb B-2 showed a significantly negative association with both progesterone and estrogen receptor presence. Progesterone receptor presence correlated significantly with survival.