The ultrastructure of water-clear cells has been described in human hyperplastic parathyroid glands. However, previous studies have failed to demonstrate this type of cell in normal human or other vertebrate parathyroid glands. Upon recently recognizing water-clear cells in the parathyroid glands of the golden hamster, we intended to examine the occurrence of these cells in other animals. In the present study the parathyroid glands of about one-year-old rabbits were observed by electron microscopy. Water-clear cells containing numerous vacuoles were demonstrated dispersed among the chief cells. The cells were generally situated close to the basal lamina of perivascular space which lay against the capillary vessel and were attached by desmosomes to the chief cells. Irregularly shaped vacuoles in the water-clear cells resembled dilated cisternae of the granular endoplasmic reticulum in the chief cells. Several ribosomes could be seen attached to the membrane of some of the irregularly shaped vacuoles. It is conceivable that the water-clear cells are transformed from the chief cells.