Diameters of secretory granules in thyrotrophs and in gonadotrophs were measured in electron micrographs of operation specimens of 4 pituitary glands and of the secretory granules in operation specimens of 10 clinically non-functioning chromophobe adenomas. The mean diameter of the thyrotroph granules was 137 ± 26 nm, of the gonadotrophs 204 ± 38 nm, of 9 of the adenomas 141 ± 20 nm and of the remaining adenoma 248 ± 67 nm. The significance of the close correlation in granule size in most of the adenomas with that of thyrotrophin granules is discussed briefly.