Christopher R. Byron, DVM, MS; Matthew C. Stewart, BVSc, PhD; Allison A. Stewart, DVM, MS; Holly C. Pondenis‌ American Journal of Veterinary Research September 2008 69 9 1129-1134 Objective—To evaluate the effects of glucosamine on equine articular chondrocytes and synoviocytes at concentrations clinically relevant to serum and synovial fluid concentrations. Sample Population—Articular cartilage and synovium with normal gross appearance from metacarpophalangeal and metatarsophalangeal joints of 8 horses (1 to 10 years of age). Procedures—In vitro chondrocyte and synoviocyte cell cultures from 8 horses were treated with glucosamine (0.1 to 20 μg/mL) with or without interleukin-1 (IL-1; 10 ng/mL) for 48 hours. Negative control cultures received no glucosamine or IL-1, and positive control cultures received only IL-1. Cultures were assayed for production of proteoglycan (via media containing sulfur 35 (35S)-labeled sodium sulfate and Alcian blue precipitation), prostaglandin E2 (PGE2; via a colorimetric assay), cyclooxygenase-2 (via real-time reverse-transcriptase PCR assay), microsomal PGE2 synthase (mPGEs; via real-time reverse-transcriptase PCR assay), and matrix metalloproteinase (MMP)-13 (via a colorimetric assay). Results—Glucosamine had no impact on proteoglycan production or MMP-13 production under noninflammatory (no IL-1) or inflammatory (with IL-1) conditions. Glucosamine at 0.1 and 0.5 μg/mL significantly decreased IL-1–stimulated production of mPGEs by chondrocytes, compared with that of positive control chondrocytes. Glucosamine at 0.1 and 5 μg/mL significantly decreased IL-1–stimulated production of mPGEs and PGE2, respectively, compared with that of positive control synoviocytes. Conclusions and Clinical Relevance—Glucosamine had limited effects on chondrocyte and synoviocyte metabolism at clinically relevant concentrations, although it did have some anti-inflammatory activity on IL-1–stimulated articular cells. Glucosamine may have use at clinically relevant concentrations in the treatment of inflammatory joint disease.