Amplification of the c-erbB-2 proto-oncogene was detected in 10% of 122 primary human breast tumors examined. Examination of patients' histories with a post-surgical median follow-up time of 53 months suggested no statistically significant association between the increased copy number of c-erbB-2 proto-oncogene in breast tumors and several oncological disease parameters, such as histopathological grading, ovarian hormonal status, age, number of positive lymph nodes, time to relapse, and survival period. Results of the analysis of matched sets of primary tumors and lymph node metastases were also consistent with the lack of a strong association between increased copy number of c-erbB-2 proto-oncogene and aggressiveness of tumors.