A surgical biopsy of an involved metacarpophalangeal joint of the hand was performed in a patient with relapsing polychondritis. Synovium and cartilage were removed and studied by light and electron microscopy. The changes in the synovium were identical to those of rheumatoid synovitis. Examination of the cartilage revealed degenerating and dead cells with lysosome and lipid accumulations in the superficial third of the articular cartilage. The middle and deeper thirds, however, contained cells lying in enlarged pericellular spaces and attached to the cytoplasm of these cells there were one or more multivesicular bodies. Some cells appeared to be ingesting a striated material having a periodicity somewhat greater than collagen. The possible significance of these findings which appear to be peculiar to relapsing polychondritis is discussed.