Intraoperative electron-beam radiation therapy (IRT) is being used to treat certain abdominal malignancies. Accurate determination of tumor size, depth, and extent is necessary to select a treatment cone of appropriate size and appropriate electron beam energy for the treatment portal. Fourteen patients undergoing evaluation for this treatment were examined with intraoperative ultrasonography (IUS) to aid therapy planning. IUS study required little additional time and readily delineated tumor size, depth, and relationship to adjacent structures. In two patients, the US and operative findings provided information that precluded use of IRT. The traditional method of tumor evaluation by intraoperative palpation and inspection was consistently enhanced by the use of IUS findings. IUS is a valuable adjunct that improves the accuracy of therapy planning for IRT.