Pro-inflammatory cytokines, matrix metalloproteinases (MMPs) and other catabolic factors participate in the pathogenesis of cartilage damage in osteoarthritis (OA). Pro-inflammatory cytokines such as interleukin-1β (IL-1β) mediate cartilage degradation and might be involved in the progression of OA. Previously, we found that haem oxygenase-1 (HO-1) is down-regulated by pro-inflammatory cytokines and up-regulated by IL-10 in OA chondrocytes. The aim of this study was to determine whether HO-1 can modify the catabolic effects of IL-1β in OA cartilage and chondrocytes. Up-regulation of HO-1 by cobalt protoporphyrin IX significantly reduced glycosaminoglycan degradation elicited by IL-1β in OA cartilage explants but increased glycosaminoglycan synthesis and the expression of collagen II in OA chondrocytes in primary culture, as determined by radiometric procedures, immunoblotting and immunocytochemistry. HO-1 decreased the activation of extracellular signal-regulated kinase 1/2. This was accompanied by a significant inhibition in MMP activity and expression of collagenases MMP-1 and MMP-13 at the protein and mRNA levels. In addition, HO-1 induction caused a significant increase in the production of insulin-like growth factor-1 and a reduction in the levels of insulin-like growth factor binding protein-3. We have shown in primary culture of chondrocytes and articular explants from OA patients that HO-1 counteracts the catabolic and anti-anabolic effects of IL-1β. Our data thus suggest that HO-1 may be a factor regulating the degradation and synthesis of extracellular matrix components in OA. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.