5 cases of small-sized insulinoma of the pancreas were studied to evaluate the ability of diagnostic imaging techniques to determine tumor location. Techniques used were extracorporeal ultrasonography, endoscopic ultrasonography (EUS), angiography, percutaneous transhepatic portal catheterization and CT. EUS was superior to the other modalities in diagnosing the location of insulinomas. We employed Color Doppler (CD) ultrasonography in one case and obtained color expression in the tumor and a pulsatile wave in the FFT analysis. Intraductal sonography of the pancreas (IDSP) was also performed in this case resulting peripheral echo-lucent, central echogenic mass. From these results, we expect that CD and IDSP will be useful in clinical application for diagnosing various tumors.