We report a 4-year experience of operative ultrasonography in 449 patients who underwent cholecystectomy for biliary lithiasis. Intraoperative uttrasonography and intraoperative cholangiography were performed in all of these patients and compared with the operative findings. The diagnostic accuracy of sonography was 97.5% and that of chalangiography was 94.4% in the patient group as a whole. The predictive value of a positive sonogram in this group was 96.4%, while that of a positive cholangiogram was lower at 86.9%. In 148 patients who underwent surgical exploration of the common duct, sonography appeared to have more accurately predicted presence or absence of stones (92.5 %) than did cholangiography (79.8%). Use of these intraoperative screening tests together led to a positive common duct exploration in 76.6% of the 148 patients, which is higher than our previous experience in which common duct exploration was performed on the basis of clinical criteria. In 7% of the 301 cholecystectomized patients, nnpredicted stones were detected at operative sonography and cholangiography. If the common duct exploration were to be performed based solely on the outcome of the sonogram, the rate of positive exploration could be 97%. Overall morbidity in this series was 9%, and retained stones following duct exploration were encountered in 1 patient. The overall mortality rate of the entire patient group was 0.9%. Operative ultrasonography of the biiiary tract as a screening procedure is, in experienced hands, a reliable method and substitute for operative cholangiography.