Preoperative B-mode ultrasonograms of the biliary system in 302 patients with cholelithiasis confirmed operatively between March 1981 and December 1986 were analyzed retrospectively in contrast to the operative findings. The results showed that during 1985-1986 the sensitivity of ultrasonography (US) to detect stones in gallbladder (GB), extrahepatic bile duct (EHD) and intrahepatic bile duct (IHD) was 98.4%, 68.2% and 82.4% respectively, each was much higher than its counterpart during the periods 1981-1982 and 1983-1984 (P less than 0.01). The specificity of US in detecting GB, EHD and IHD stones was all over 90% during the latter two years. The observations made in the present study suggest that the accuracy of US has risen so significantly that it should be used as the first modality in diagnosing cholelithiasis, particularly cholecystolithiasis. It, however, should be supplemented with such tests as oral cholecystography, intravenous cholangiography, percutaneous transhepatic cholangiography (PTC), endoscopic retrograde cholangiopancreatography (ERCP) to establish a correct diagnosis when its interpretation is equivocal.