By immunohistochemical staining C-erbB-2 (neu) oncogene was found on the cell membrane in 19 out of 44 primary breast cancers from a pathology archive. No obvious relation was found between neu oncogene, age, and lymph node status and tumor size. There was a tendency towards smaller primary tumors and more estrogen receptor-negative tumors in the oncogene-positive group. No case of distant metastasis during follow-up was found among the oncogene-negative patients, while 6 oncogene-positive patients developed such metastases. This suggests that the neu oncogene is an independent prognostic factor, which might predict the development of distant metastasis. Further studies including more patients and long-term survival analysis are, however, needed in order to evaluate the prognostic significance of the neu oncogene.