Articular cartilage fragments were added to monolayer cultures of synovial membrane cells. After 3 wk of incubation, the cartilage fragments were examined histologically for metachromasia and basophilia, and for fluorescent staining using a rabbit antiserum to cartilage protein-polysaccharide. Cartilage incubated with cells derived from rheumatoid synovial membranes showed striking loss of metachromasia and basophilia as well as diminished to absent fluorescent staining. Cartilage fragments incubated with cells from normal synovia, or with cells from the synovial membrane of a patient with Reiter's syndrome, did not show these changes and resembled control cartilage incubated in tissue culture medium alone. It appears, therefore, that rheumatoid synovial cells in tissue culture are able to deplete the matrix of articular cartilage.