The shoulder capsule and labrum of Japanese macaque monkeys were studied immunohistochemically with the use of antisera against protein gene product 9.5 (PGP 9.5), calcitonin gene-related peptide (CGRP), and substance P (SP) to further characterize the innervation of the supporting structures of the shoulder joint. With PGP 9.5 immunohistochemistry thick nerve fibers (diameter > or = 10 microm) presumed to be proprioceptive based on topographic location were found to be abundant in the posterior half of the capsule. Thinner fibers (diameter <10 microm) presumed to contain nociceptive and autonomic fibers were located in the posterior half of the capsule. Ruffini-like corpuscles were predominantly located in the inferior portion of the capsule. SP and CGRP immunoreactive thin fibers presumed to be nociceptive were abundant in the posterior half of the capsule. Thin fibers that appeared to be nociceptive fibers were found in the marginal portion and the parenchyma of the labrum, although the number was small. The predominant distribution of the Ruffini-like corpuscles in the inferior portion of the capsule suggest an important role of the inferior portion in generation of the proprioceptive output, which should be advantageous in stabilization of the joint in motion. The abundance of nociceptive fibers in the posterior half of the capsule may be responsible for the pathophysiological transmission of pain around the shoulder joint.