Quantitative DNA dot blot hybridization and immunohistochemical method were employed to detect amplification and overexpression of proto-oncogene c-erbB2 in 101 paraffin-embedded breast cancers. The results showed that c-erbB2 was amplified and overexpressed in 34.7% and 23.8% of examined cases respectively. The overexpression of c-erbB2 was correlated with, but not always paralled to the gene amplification. The moderate to high-level overexpression of c-erbB2 detected by immunohistochemistry was significantly associated with the size of the tumour and the number of lymph nodes involved. No differences were found in the alteratio of c-erbB2 gene and its protein expression between primary and metastatic breast cancers indicating that the genotypic and phenotypic changes of c-erbB2 occured prior to and maintained in the process of metastasis of breast cancer.