Three lysosomal polysaccharidases were measured in synovial fluid (SF) and serum from rheumatoid (RA) patients, SF from osteoarthritic (OA) patients, and serum from healthy volunteers. (1) There was no correlation between the enzyme levels and white cell counts in the SF. (2) beta-glucuronidase and beta-N-acetylglucosaminidase were markedly elevated in the SF of RA as compared to OA. (3) beta-glucuronidase and beta-N-acetylglucosaminidase levels in the SF of RA correlated well with each other but not with hyaluronidase. (4) beta-glucuronidase and beta-N-acetylglucosaminidase levels were higher in the SF of RA than in the corresponding serum, while the converse was true for hyaluronidase. (5) Hyaluronidase levels were significantly higher in RA serum than in normal serum. These results suggest that the synovial membrane may be the source of beta-glucuronidase and beta-N-acetylglucosaminidase, while hyaluronidase is derived from a source remote from the joint via the serum. This source of hyaluronidase may be the liver. (J Rheumatol 2: 393-400, 1975).