Serial sections of 90 Sprague-Dawley rat brains with the pineal in situ were scanned to determine the occurrence and regional distribution of calcareous concretions within the pineal gland and its surrounding leptomeningeal tissue. In 90% of the cases examined concretions were found in varying number and appearance, predominantly lying in the dorsal region of the pineal gland and in the distal portion of the pineal stalk. Discussing the hypothesis advanced by Lukaszyk and Reiter (1975) that the origin of pineal concretions may be related to a neurosecretory process involving a pineal carrier protein, called neuroepiphysin, it is thought that, in view of the intra- and extra-pineal occurrence of concretions, processes other than secretion should be considered. Since in the pineal organ lymphatics are lacking it may well be that, due to a reduced drainage of tissue fluid, the coagulation of intercellular organic debris mingled with minerals increases with age.