AbstractThe adenohypophysis of a newborn with cyclopia was examined by electron microscopy. The hypophysis was normal in size and shape in the present case. Electron microscopy, however, showed degenerating cells in the adenohypophysis. These cells had small number of granules and cytoplasmic organelles, and the concentric membranous structure, but were not considered as necrotic cells. These findings may indicate overproduction of hormones by the damage of the negative feedback system. No remarkable change, however, was observed in the endocrine organs by light microscopy. Thus, the possible disorder of the hormone production might not be severe enough to cause abnormal formation of the endocrine system in the present case.