In 72 patients with malignant neoplasms of uterine body the serum concentration was determined of CA 125 antigen. In 38 cases serum samples were taken before oncological treatment and in 34 cases after the first stage of treatment. It was found that CA 125 concentration was significantly higher in patients before the treatment, with higher values in more advanced cases and in poorly differentiated tumours. The sensitivity of the CA 125 test was however low in the studied material (19.4%) at cut-off threshold 35 IU/ml, and routine determination of this antigen in serum to be without diagnostic value in uterine body malignancy.