The pathology of the parathyroid glands in two cases in which hyperparathyroidism was associated with chronic renal disease and 10 in which the association was with the malabsorption syndrome is described. It is concluded that whereas in chronic renal disease the development of an autonomous adenoma may be preceded by anatomical secondary diffuse hyperplasia such a stage is not proven when the adenomas develop against a background of the malabsorption syndrome. The importance of this latter association is stressed.