Leydig cell hyperplasia.

The ultrastructure of Leydig cell hyperplasia is described. The hyperplastic Leydig cells differ morphologically from normal Leydig cells as well as from Leydig tumor cells. They have less smooth endoplasmic reticulum and less lipofuscin pigment in their cytoplasm, and the nuclear membrane shows more irregular indentations than normal Leydig cells. It is suggested that electron microscopy might be useful in the differential diagnosis between Leydig cell hyperplasia, Leydig cell tumors, and normal Leydig cells.