In patients with pathology to cruciate ligaments, menisci and cartilage and in some patients with symptomatic knees without gross intraarticular changes, proteoglycan fragment concentrations in joint fluid and inflammatory reaction of the synovium were related to the cartilage condition. There was a weak positive correlation between increased concentrations of proteoglycan fragments in joint fluid and the degree of cartilage degeneration, indicating higher concentrations in knees with more advanced cartilage destruction, but there was no correlation to the synovial reaction at histological inspection. However, in most knees the synovial tissue was infiltrated by inflammatory cells. Symptomatic knees free from gross intraarticular pathology showed similar synovial changes and concentrations of proteoglycan fragments in joint fluid as knees with intraarticular pathology and obvious cartilage degeneration. The complex process of proteoglycan synthesis, release, degradation, and clearance from joint fluid apparently caused the weak or absent correlations between this 'marker' protein and the degree of synovitis and arthrosis stage.