Ninety-eight patients treated for breast carcinomas were followed from 54 to 75 months after primary diagnosis. All had undergone a modified radical mastectomy with removal of axillary lymph nodes. 36 breast carcinomas were NSE-positive and 62 were negative. NSE-positive tumours were significantly more frequently estrogen receptor-positive than the NSE-negative tumours, and the estrogen receptor values were higher in the NSE-positive groups. Patients with NSE-positive tumours and patients with NSE-negative tumours did not differ with regard to presence of lymph node metastases at the time of primary surgery. However, the study showed that patients with NSE-positive tumours had a tendency towards more lymph node metastases after primary surgical intervention, but a better outcome than patients with NSE-negative tumours and metastases. This study, with a 5-year follow up, failed to demonstrate any major prognostic significance of immunostaining for NSE.