IN A REVIEW of the ultrastructual organization of human acidophil and chromophobe pituitary adenomas, the acidophils were from abundantly to sparsely supplied with secretory granules measuring 300 to 500 mμ, and the secretory granules in chromophobe adenomas were of two sizes, the average diameter being about 100 mμ in some cells and approximately 300 mμ in others. 1-3 Pituitary adenomas from 50 patients with acromegaly were subdivided by Young et al 4 into two groups designated as typical (6 cases) and atypical (44 cases) adenomas on the basis of staining with azure-eosin, PAS orange G, and Mallory Heidenhain methods. The atypical adenomas were composed of moderately or sparsely granulated acidophils and agranular cells that were indistinguishable from chromophobes. Herlant and his co-workers, 5-9 with the light microscope, studied the changes which occurred in the pituitaries of various animals during their reproductive cycles, and five functional classes of cells were differentiated in