Effects of glucosides of chaenomeles speciosa (GCS)-a Chinese traditional herbal medicine (CTM) on inflammatory and immune responses and its mechanisms in collagen-induced arthritis (CIA) rat were studied. Hind paw volumes of rats were measured by volume meter; lymphocyte proliferation, interleukin-1, interleukin-2, TNF-alpha level was determined by 3-(4,5-2 dimethylthiazal-2yl)2,5-diphenyltetrazoliumbromide (MTT) assay; cAMP level in synoviocytes was analyzed by competitive protein binding assay (CPBA). mRNA expression of G(i,), G(s), and TNF-alpha of synoviocytes in CIA rats was measured by RT-PCR and antibodies to collagen type II (CII) were determined by enzyme-linked immunosorbent assay (ELISA), respectively. There was a marked secondary inflammatory response in CIA model, which accompanied with the decrease of body weight and the weight of immune organs simultaneously. The administration of GCS (30, 60, 120 mg x kg(-1), ig x 7 days) inhibited the inflammatory response and restored body weight and the weight of immune organs of CIA rats. Lymphocyte proliferation and IL-2 production of CIA rats increases, together with IL-1 and TNF-alpha in peritoneal macrophages and synoviocytes. The administration of GCS (30, 60, 120 mg x kg(-1), ig x 7 days) reduced above changes significantly. GCS at the concentration of 0.5, 2.5, 12.5, 62.5, 125 mg x l(-1) increased cAMP level of synoviocytes, which decreased in CIA rats in vitro. At the same time, GCS inhibited mRNA expression of G(i,) and TNF-alpha of synoviocytes and increased mRNA expression of G(s) of synoviocytes in CIA rats. GCS had no effect on the concentration of antibodies to CII. GCS possesses anti-inflammatory and immunoregulatory actions and has a therapeutic effect on CIA rats due to G protein-AC-cAMP transmembrane signal transduction of synoviocytes, which play a crucial role in pathogenesis of this disease.