Purpose : To investigate the usefulness of dynamic MR imaging in the diagnosis of pituitary microadenomas.Materials and Methods : Dynamic MR imaging was performed in 31 patients with suspicious pituitary microadenoma.The MR examination was performed on a 2.0T or 1.5T superconductive MR unit using spin echo(SE) technique with arepetition time of 200msec, echo time of 15 msec, 128 $ imes$ 256 matrix and one excitation. Actual sampling time perimage was 26 seconds. The field of view was 25cm and a section thickness of 3mm with 2mm gap was chosen. After arapid hand injection(2-3ml/sec) of Gd-DTPA(0.1 mmol/kg of body weight), dynamic coronal plane MR images wereobtained every 20-30 seconds for 3-5 minutes. Between never and ten serial images were usually obtained. Afterdynamic MR imaging, routine SE T1-weighted images(T1WI) were obtained in the same plane as dynamic images, anddetection rates of pituitary microadenoma using dynamic MR imaging and using routine enhanced T1WI, wereretrospectively compared. Results : On early dynamic images(30$mid$90 seconds), 23 of 31 adenomas(74.2%) were wellvisualized, with a clear border ; of particular note is the fact that 11 of the 31 were well visualized at30-second dynamic image. On late dynamic images(120-180 seconds), six microadeomas(19.4%) were well-visualized and; two(6.5%) were well-visualized throughout on all dynamic images. Meanwhile, 12 of 31 microadenomas(38.7%) werewell-visualized on routine Gd-DTPA enhanced T1WI. Conclusion : Dynamic MR imaging with Gd-DTPA bolus injection wasthe most useful technique for the detection of pituitary microadenomas, especially on early-phase dynamic images.