To know the effects of Gentiana macrophylla(GM) on the immune response, this study was undertaken. GM is one of the well-known oriental medicines for a lomg time used for the treatment of such diseases as arthralgia, headache, hepatitis, SLE, hemiparesis, and so on. To evaluate the effects of GM on immune response in the collagen induced arthritis, phagocytic activity of macrophages, proliferation of T-lymphocytes, secretion of nitric oxide in urine, and production of ROIs, $TNF-{alpha}$ and nitric oxide in synoviocytes were measured. The results obtained in this study were as follows: 1. During the progress of CIA, the administration of GM enhanced phagocytic activity of macrophages in vivo and vitro. 2. During the progress of CIA, the administration of GM inhibited production of ROIs in synoviocytes. 3. During the progress of CIA, the administration of GM inhibited production of TNF- a in synoviocytes. 4. During the progress of CIA, the administration of GM inhibited proliferation of T lymphocytes. 5. During the progress of CIA, the administration of GM inhibited production of nitric oxide in synoviocytes. 6. During the progress of CIA, the administration of GM inhibited secretion of nitric oxide in urine. According to the above results, during the progress of CIA, it might be considered that GM has a curative effect on rheumatoid arthritis by controling immune response.