c-myc, c-erbB-2, and Ki-67 expression was examined by immunohistochemistry in 11 normal breast tissues and 42 invasive and 14 noninvasive breast carcinomas. The c-myc product was detected in all breast carcinoma specimens and in 7 of 11 normal breast tissues. Invasive tumors stained more frequently with the anti-myc monoclonal antibody than did noninvasive tumors, while the level of expression in normal breast tissue was much less than that in breast cancer. Membrane staining of the c-erbB-2 protein was demonstrated in 29% (4 of 14) of noninvasive ductal carcinomas and in 45% (19 of 42) of invasive breast carcinomas. None of the 11 normal breast tissue samples was positive. The mean value of Ki-67-positive cells was 0.91 +/- 0.31% for normal breast tissue, 4.57 +/- 1.36% for noninvasive ductal carcinoma, and 12.76 +/- 2.18% for invasive breast cancer. In 42 invasive breast carcinomas, the expression of c-myc, c-erbB-2, and Ki-67 proliferation marker were compared with lymph node status, estrogen receptor status, progesterone receptor status, and age of patients at diagnosis. c-erbB-2 overexpression and Ki-67 overexpression were identified as the only factors associated with lymph node status. We concluded that they might be additional prognostic factors for breast carcinoma.