['To examine if changes in serum cartilage oligomeric matrix protein (COMP) correlate with the development of cartilage damage, as measured by histological grading, in corticosteroid-treated animals with collagen-induced arthritis (CIA).', 'DA rats with established CIA were treated with corticosteroids (betamethasone, 0.1 mg/kg body weight) or placebo (saline) intraperitoneally once daily after reaching an arthritis score exceeding 1. The treatment continued throughout the study. Arthritis progression was monitored by clinical scoring of paws, serial measurements of serum COMP and fibrinogen, and histological grading of paws.', 'Corticosteroid treatment reduced clinical signs of arthritis compared with placebo (arthritis score reduced, P < 0.01 at day 25). Corticosteroid treatment also reduced fibrinogen levels compared with placebo (P < 0.01). The morphological changes in the joint were less severe in the corticosteroid-treated animals (median cartilage score 4 in the placebo group, 0 in the corticosteroid-treated group; P < 0.01). The levels of COMP remained unchanged during treatment in the corticosteroid-treated arthritic animals, whereas an increase in levels of COMP was observed in rats treated with placebo (P < 0.01). There was a correlation between serum COMP and the extent of cartilage destruction at day 25 after immunization (r = 0.77, P < 0.001).'] Does corticosteroid treatment of experimental arthritis retard cartilage destruction as determined by histology and serum COMP?