This study aims to investigate and compare the inflammation specific laboratory findings as well as routine biochemical laboratory parameters between rheumatoid arthritis and osteoarthritis patients. Thirty-four patients with rheumatoid arthritis and 34 patients with osteoarthritis were included in the study. Patients in the acute phase were excluded. In the laboratory investigation of both groups, leucocyte, erythrocyte and platelet counts; haemoglobine level, haematocrite value, sedimentation rate; levels of triglyceride, cholesterol, calcium, phosphour, alkaline phosphatase, blood glucose, urea, creatinine, uric acid, alanine aminotransferase and aspartate aminotransferase in blood serum were evaluated and comparison were made between the groups. Any probable correlation between the laboratory parameters and clinical parameters like disease duration and  joint count was assessed. Independent samples t test and Pearson correlation analysis were used in the statistical analysis. When compared with osteoarthritis group, patients with rheumatoid arthritis had higher values of leucocyte count, erythrocyte count, alkaline phosphatase level, and sedimentation rate and lower values of erytrocyte count, haemoglobine, haematocrite, triglyceride, cholesterol, uric acid and calcium levels. No difference was found in the levels of phosphor, blood glucose, urea, creatinine, alanine aminotransferase and aspartate aminotransferase. Correlation was not found between laboratory and clinical parameters. Detailed laboratory investigation in rheumatoid arthritis and osteoarthritis patients will contribute to our understanding of the etiopathogenesis of these diseases.