CA125 is a coelomic epithelial antigen which is widely used to monitor residual disease in patients undergoing chemotherapy for ovarian cancer. Interpretation of serum CA125 levels has been based on a normal value of 35 U/ml which was derived by screening a young, general population of blood donors which included women with intact reproductive systems. This study addresses the issue of what constitutes a normal serum CA125 level following successful surgical therapy for gynecologic malignancy. Three hundred ninety-three CA125 values were measured in 145 patients after an elapsed time of at least 1 year following completion of surgical therapy for early-stage endometrial or cervical adenocarcinoma. All patients were without evidence of recurrent disease. The mean duration of followup was 4.3 years with a median of 3.7 years. Sixty-seven percent of the CA125 values were less than 10 U/ml; 95% were less than or equal to 20 U/ml. The median value for this patient population was 7.5 U/ml with a mode of 7.1 U/ml. There was no correlation between patient age and CA125 levels. These data suggest that the normal value for CA125 used for patient follow-up after treatment for gynecologic adenocarcinoma needs to be redefined. Our data support an upper limit of normal of 20 U/ml and encourage further study on the clinical impact of this new definition.