The two parenchymal cell types, the chief cells and the oxyphil cells, have been recognized in electron micrographs. The chief cells contain within their cytoplasm mitochondria, endoplasmic reticulum, and Golgi bodies similar to those found in other endocrine tissues as well as frequent PAS-positive granules. The juxtanuclear body of the light microscopists is identified with stacks of parallel lamellar elements of the endoplasmic reticulum of the ergastoplasmic or granular type.

Oxyphil cells are characterized by juxtanuclear bodies and by numerous mitochondria found throughout their cytoplasm. Puzzling lamellar whorls are described in the cytoplasm of some oxyphil cells.

The endothelium of parathyroid capillaries is extremely thin in some areas and contains numerous fenestrations as well as an extensive system of vesicles. The possible significance of these structures is discussed.

The connective tissue elements found in the perivascular spaces of macaque parathyroid are described.