PURPOSE: To determine whether dynamic or conventional MR imaging is most useful for the detection of pituitary microadenoma. MATERIALS AND METHODS: The study involved 20 patients (M:F=1:19, mean age=37 years) in whom a pituitary microadenoma had been identified. Routine unenhanced coronal T1-weighted MR imaging was followed by dynamic imaging (repetition time/echo time/excitation=200/10/1, 3-mm-thick sections, 256X128 or 256 ma-trix,14X14-cm field of view, scan time=30 or 60 seconds, spin-echo pulse sequence), and contrast-enhanced coronal T1-weighted imaging was then immediately performed. Temporal changes in signal intensity were quantified with manually placed ROIs (regions of interest, circular, 3 mm 2), and tissue contrast between the pituitary gland and microadenoma was calculated. Conspicuity of the tumor margin was graded by three radiologists working independently as either 4 (excellent clear margin), 3 (good clear margin), 2 (relatively clear mar-gin), or 1 (unclear margin). RESULTS: Average peak enhancement of the pituitary gland and microadenoma occurred at 58.5 and 91.5 seconds, respectively. Maximum enhancement of the pituitary gland occurred within 30 to 60 seconds of contrast infusion (signal intensity range: 426-442), but during dynamic MR imaging, the microadenoma showed rela-tively constant enhancement (signal intensity range: 230 -250). Maximal contrast between normal pituitary gland and the microadenoma was seen at 60 seconds or in the first three sequential images. Dynamic MR images were superior to conventional T1-weighted images, with or without contrast infusion, not only in terms of tissue contrast between the pituitary gland and the microadenoma (p=0.0048), but also as regards tumor margin conspicuity (p=0.0035). CONCLUSION: Dynamic MR imaging is a useful technique in the detection of pituitary microadenoma.