The concentration of carcinoembryonic antigen and alpha-lactalbumin in tumor tissue cytosol were analyzed in a group of 19 tumors of cystosarcoma phyllodes type. Both antigens were also localized in the tissue of identical tumors by means of immunohistochemical procedure. The cytosol levels of both proteins were found to be higher in the histologically defined malignant type of phylloid tumors. This group was also characterized by the simultaneous occurrence of both antigens. We did not manage to prove any relationship between the presence of alpha-lactalbumin and the steroid hormone receptor positivity in tumor tissue.