In a study comprising 40 patients with pituitary macroadenomas, MR imaging was performed before and after administration of Gd-DTPA. Before contrast administration T1- and T2-weighted images were obtained, and after the injection, frontal and/or sagittal T1-weighted images. Tumour extension and delineation, relationship to adjacent structures, and signal intensity patterns were evaluated. Compared with pre-contrast T1-weighted images only, post-contrast images provided considerable additional information, but not infrequently this information could also be extracted from pre-contrast T2-weighted images. Post-contrast images were superior regarding the tumour relationship to the cavernous sinus and to the normal pituitary tissue. T2-weighted images were helpful in the diagnosis of degenerative changes, in particular intratumoural haemorrhage. A positive correlation was found between the T2 value (from dual echo sequences) and the degree of enhancement in areas with an appearance of solid tumour tissue, and the enhancement was significantly lower in GH-secreting tumours than in non-secreting ones. It is concluded that the use of Gd-DTPA is often justified in pituitary macroadenomas, particularly in pre-operative evaluation.