Arthroscopy was performed on 18 patients (19 joints) with temporomandibular joint arthropathy. Arthroscopic investigation revealed that 12 patients had disk derangement, including 3 patients with rheumatoid arthritis. Six patients had osteoarthrosis, including one patient with rheumatoid arthritis. Synovial fluid content of substance P-like immunoreactivity (SP-LI), neurokinin A (NKA-LI), calcitonin gene-related peptide (CGRP-LI), neuropeptide Y (NPY-LI) and vasoactive intestinal polypeptide (VIP-LI) were analysed using radioimmunoassay technique. All peptides analysed were found, although in various concentrations, in the different joints. There were no significant differences in concentrations of the peptides in the synovial fluid between patients in the various groups. No significant correlation was found between clinical symptoms and signs, arthroscopic findings, or use of analgesic/anti-inflammatory medication versus concentrations of peptides in the synovial fluid. In comparison with earlier findings in the knee joint significantly higher concentrations of SP-LI, CGRP-LI and NPY-LI were found in the TMJ.