The presence of luteinizing-hormone-releasing hormone (LHRH)-like and alpha-melanocyte-stimulating hormone (alpha-MSH)-like immunoreactive fibers, nerve terminals or cellular elements in the pineal gland of the sheep has been investigated by immunohistochemistry. No LHRH-or alpha-MSH-like immunoreactive fiber, nerve terminals or cellular elements have been demonstrated in the pineal organ of the sheep. However, LHRH- and alpha-MSH-like immunoreactive fibers are present in the posterior commissure. Immunoreactive LHRH and alpha-MSH nerve endings are evident in the medial and lateral habenular nuclei. Discrepancies with the results obtained in other mammals are indicative of species differences in the distribution of LHRH- and alpha-MSH-like immunoreactive material in the pineal region.