Adult human articular cartilage has been maintained in organ culture for 8 days, and the culture medium, which was changed on alternate days, was pooled. Normal and rheumatoid cartilage was obtained from patients and 4 types of culture were prepared: (1) cartilage alone; (2) cartilage + D-penicillamine; (3) cartilage + homologous synovium; (4) cartilage, synovium, and D-penicillamine. The hexosamines and hexuronic acid were measured in the cartilage explants and in the medium. The quantity released was divided by the amount measured in the original cartilage explant and the different culture variables were compared. D-penicillamine did not alter the release of cartilage proteoglycan, but the addition of synovium did. The rheumatoid cartilage released significantly more proteoglycan than normal cartilage whether or not homologous synovium was present.