The authors evaluated the levels of a mucinous-like carcinoma antigen (M.C.A.) in the serum of 105 follow-up patients with breast carcinoma by means of an enzyme immunoassay. The negative/positive cut-off level determined in a group of healthy women was 13.2 U/ml. 80 patients turned out to be free disease, while 25 patients showed relapse or metastasis. High levels of MCA were observed in 72.0% of the patients with renewal of the neoplastic disease as well as in 12.5% of the free disease subjects. The EIA method appeared to have a good specificity (87.5%) and a fair test efficiency (83.8%). On the contrary, its sensitivity (72.0%) and its predictive value (64.3%) were not completely satisfactory. Therefore we think the matter needs to be studied more deeply and so does the case-report.