1. Nucleosides and bases in physiological fluids result from metabolism of nucleic acids and nucleotides and from dietary sources. As nucleotide catabolism increases during tissue injury, nucleosides and bases could serve as useful biochemical markers in arthritis.
2. We have quantified nucleosides and bases in synovial fluid and plasma by high-performance liquid chromatography in order to examine whether nucleotide metabolism is increased in patients with rheumatoid arthritis and osteoarthritis.
3. At least ten u.v.-absorbing compounds were detected in plasma and synovial fluid; only urate, creatinine, hypoxanthine and uridine were present in identifiable and quantifiable amounts.
4. In synovial fluid from patients with rheumatoid arthritis the concentration of hypoxanthine was increased and that of urate decreased compared with osteoarthritis.
5. These data suggest that there is an increase in purine metabolism in the rheumatoid arthritis joint and that hypoxanthine is a potential marker of synovitis.