The specific monoclonal antibody, DF3, for breast cancer and the corresponding tumor marker CA15-3 were evaluated in 108 patients with primary cancer of the breast. These antigens correlated poorly with the known prognostic parameters. Elevated CA15-3 serum values were associated with the cytoplasmic distribution of the DF3 antigen in the cell. The DF3 distribution pattern and the CA15-3 serum values had prognostic significance for disease-free interval.