For assessment of the value of delayed hepatobiliary imaging with technetium 99m (99mTc)-(Sn)-N-pyridoxyl-5-methyltryptophan (99mTc-PMT) for specific diagnosis of hepatocellular carcinoma, 88 patients with various malignant and benign liver diseases (49 with hepatocellular carcinoma, 4 with cholangiocellular carcinoma, 10 with metastatic liver carcinoma, 2 with liver cysts, 2 with liver hemangioma, 1 with liver abscess, 2 with intrahepatic lithiasis, 12 with liver cirrhosis, and 6 with chronic hepatitis) were studied. In 20 (41%) of the 49 patients with hepatocellular carcinoma, greater uptake of 99mTc-PMT by the tumor than by the surrounding liver tissue was seen in delayed hepatobiliary images, whereas in eight patients (16%), equilibrated uptake was seen. No increased uptake of the radioisotope by hepatic lesions was seen in 21 patients with localized liver diseases other than hepatoma. Moreover, in 18 patients with diffuse liver diseases, no focal accumulation of the radioisotope was seen in delayed 99mTc-PMT images. In addition, of 28 patients with hepatocellular carcinoma in whom the serum alpha-fetoprotein level showed little or no increase, 12 showed increased uptake of 99mTc-PMT by the tumor. In assessing delayed 99mTc-PMT images, however, it was necessary to consider following complications: accumulation of tracer in obstructed and dilated biliary trees; retention of radioactivity in nonneoplastic liver tissues; difficulties in evaluating 99mTc-PMT uptake by small hepatic tumors; overlapping of radioactivity in the gut and gallbladder in delayed 99mTc-PMT images of tumors. This study indicates that delayed 99mTc-PMT images can be useful in the diagnosis of hepatocellular carcinoma.