Objective - This study attempts to evaluate the status of oxidative stress in osteoarthritis (OA), by measuring some parameters of oxidant stress and antioxidant defenses in blood, before and after homeopathy treatment, and to asses the role, if any, of homeopathic treatment in modulating free radical toxicity in OA.Methods - Erythrocyte lipid peroxidation (LP), erythrocyte antioxidants viz., glutathione (GSH), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CT) and plasma antioxidants viz., ceruloplasmin, glutathione-S-transferase (GST), vitamin C, total antioxidant activity (AOA) were determined in eighty one patients with OA and fifty three normals. Forty seven patients, who were treated with homeopathic remedies were considered for the follow-up studies.Location - Father Muller Homeopathic Hospital, Mangalore, South Karnataka, India.Results - Erythrocyte LP (0 hour, p < 0.001; 2 hours, p < 0.01; and susceptibility to LP, p < 0.05) and SOD (p < 0.05) were significantly higher, whereas plasma vitamin C (p < 0.01) and AOA (p < 0.001) were significantly lower in OA patients when compared to controls. In follow-up patients the erythrocyte LP (0 hour, p < 0.01; 2 hours, p < 0.01; and susceptibility to LP, p < 0.01) and SOD (p < 0.01) were significantly lower when compared to their pretreatment values. Plasma vitamin C attained a normal range. The AOA activity after treatment was not significantly different from that observed before treatment.Conclusion - Oxidative stress increased in OA as indicated by increased LP, SOD, decreased vitamin C and AOA. On homeopathic treatment the LP has decreased in the erythrocytes which shows and reduced oxidative stress. This is further evidenced by returning of plasma vitamin C and erythrocyte SOD to the normal levels, but oxidant stress has not been completely overcome as plasma AOA remained low after treatment.