Serial sections of pig pineal glands were stained with von Kossa's and Alizarin red S methods to determine the occurrence and localization of calcified concretions. In the pineal glands of pigs aged eight months, concretions were not found. A small number of concretions was observed in all investigated pineal glands of three years old pigs. The concretions were distributed in the connective tissue of the pineal capsule and septa. The potassium pyroantimonate method was used for ultracytochemical localization of calcium ions. In pinealocytes, precipitates were observed in nuclei, mitochondria, Golgi apparatus, endoplasmic reticulum and cytoplasmic matrix. Single precipitates were found on the outer membranes of dense bodies, multivesicular bodies and lysosomes. There were no differences in the amount or the localization of precipitates between dark and light pinealocytes and between pinealocytes of animals aged both eight months and three years. The results suggest that: (1) the calcified concretions in the pig pineal gland are formed by the leptomeningeal tissue without participation of the pinealocytes, (2) cytoplasmic dense bodies, specific components of the pig pineal gland, are only slightly involved in calcium turnover in the pinealocytes.