Ultrastructure of oncocytic adenoma of the human pituitary gland

Summary Two cases of oncocytic adenoma occurring in the pituitary are reported. Both were men aged 40 and 50 years respectively and there was no evidence of endocrine abnormality.In both the tumours many cells showed abundant acidophilic finely granular cytoplasm which had not stained positively with PAS-orange G stain. Electron microscopically the cells contained numerous mitochondria associated with marked reduction of other cytoplasmic organelles including the secretory granules.