We studied the cellular localization of amylase in normal Fallopian tubes and serous ovarian neoplasms using an indirect immunoperoxidase technique. The primary antiserum was against human pancreatic amylase, and was found to inhibit ovarian tumor amylase as well. Amylase was present in normal endosalpingeal epithelium and in the epithelial cells of benign, borderline, and malignant serous ovarian tumors. A mucinous cystadenoma was also studied and contained no amylase. This localization suggests that amylase production by serous ovarian neoplasms reflects the endosalpingeal differentiation of these tumors. Antibody to amylase may be potentially useful in distinguishing serous ovarian tumors from other forms of ovarian neoplasia.