Objective - To determine the effects of glucosamine (GLN) and chondroitin sulfate (CS), at concentrations attainable in vivo, on expression of genes encoding proteolytic enzymes, enzyme inhibitors, and macromolecules of articular cartilage in interleukin-1(IL-1)-challenged bovine cartilage explants. Sample population - Articular cartilage explants harvested from 9 steers. Procedures - Cartilage explants were exposed to media containing 10% fetal bovine serum (FBS) only, IL-1 (50 ng/mL), IL-1 with GLN (5 μg /mL), IL-1 with CS (20 μg/mL), or IL-1 with GLN and CS for 24 and 48 hours. Cartilage was frozen, and RNA was extracted. Gene expression of matrix metalloproteinases (MMPs)-2, -3, -9, -13, and -14; aggrecanases (Aggs)-1 and -2; tissue inhibitors of metalloproteinases (TIMPs)-1, -2, and -3; and type II collagen and aggrecan were assessed with quantitative real-time polymerase chain reaction. Results - Upregulated MMP-3, MMP-13, and Agg-1 transcripts at 24 hours were repressed by the GLN and CS combination by at least approximately 6-fold. Glucosamine was effective in suppressing IL-1-induced mRNA expression of MMP-13, Agg-1, and Agg-2, whereas CS was effective in decreasing IL-1-induced MMP-13 transcript at 24 hours. At 48 hours, GLN and CS added separately and in combination significantly abrogated Agg-1 and Agg-2 gene induction. The combination also decreased IL-1-stimulated MMP-13 transcript. Conclusions and clinical relevance - GLN and CS, at concentrations that are within the range measured in synovial fluid and blood after oral administration, may regulate expression of matrix degrading enzymes and their inhibitors at the transcriptional level, providing a plausible mechanism for their purported chondroprotective properties.