The serum levels of carcino-embryonic antigen, tissue polypeptide antigen (TPA), breast carcinoma antigen 15-3 and mucin-like carcinoma-associated antigen were measured pre-operatively in 99 patients with breast cancer receiving no adjuvant hormonal or chemotherapy and in 64 patients with benign breast tumours. Using the 95th percentile of the marker levels in patients with benign breast tumours as the cut-off level, marker levels in patients with breast cancer were related to prognosis. In the follow-up period of 6-36 months (mean = 17.9 months), 20 out of the 99 patients developed metastases. Only 4 out of these 20 patients had elevated pre-operative levels of one or more of the markers. One out of these 4 patients was misclassified having metastatic disease at the time of the operation. On the other hand, in a total of 28 patients the pre-operative levels of one or more markers were noted to be elevated; 26 of the patients remained disease-free at the time of follow-up.