Increased kynurenine/tryptophan-reflects trytophan degradation-and neopterin levels have been regarded as a biochemical marker of cell-mediated immune response and inflammation. This study was designed to evaluate the usefulness of tryptophan degradation and neopterin levels in active rheumatoid arthritis patients under therapy. In this case-control study, kynurenine and tryptophan levels were determined by HPLC; neopterin and tumor necrosis factor-a levels were measured with ELISA in 32 active rheumatoid arthritis patients and 20 healthy controls. Although mean values of tryptophan, kynurenine, ratio of kynurenine to tryptophan, neopterin, and tumor necrosis factor-a levels did not show statistically significant differences between patient and control groups, neopterin levels correlated positively with kynurenine (r=0.582, p<0.02), kynurenine/tryptophan (r=0.486, p<0.05), erythrocyte sedimentation rate (r=0.472, p<0.05) and RF (r=0.478, p<0.05) in the rheumatoid arthritis group. CRP levels of the patient group correlated with kynurenine levels (r=0.524, p<0.03). Determination of tryptophan degradation and neopterin levels in chronic inflammatory disease may provide a better understanding of progression of the disease.