Serial CA125 measurements in 169 patients with epithelial ovarian carcinoma were obtained. Changes in serum CA125 measurements are shown to reflect changes in clinical status. For patients with macroscopic disease receiving chemotherapy, the sensitivity and specificity for predicting response are shown to be 95% and 86% respectively. For patients with no known disease, the sensitivity and specificity for detecting relapse are shown to be 86% and 91% respectively. The clinical correlates with the level of serum CA125 were examined and the most important is shown to be amount of residual disease.