Hyperthyroidism is associated with increased bone turnover. Besides the hormones of calcium metabolism , locally produced factors are important in maintaining normal bone metabolism. Interleukin-6 (IL-6), in particular, has a major influence on bone turnover. In this study, serum IL-6 and tumor necrosis factor-alpha (TNF-alpha) levels, as well as bone turnover markers and relationships between them, were investigated in hyperthyroidism and hypothyroidism. A total of 20 female patients with hyperthyroidism, 15 with subclinical hyperthyroidism, 16 with hypothyroidism, and 15 with subclinical hypothyroidism constituted the patient groups. In all, 15 age-matched healthy female volunteers were recruited as controls. When compared with controls, serum TNF-a levels showed no significant difference in any of the patient groups (P >.05). In the groups with hyperthyroidism and subclinical hyperthyroidism, IL-6 levels were significantly higher compared with control group values (P <.05). Hyperthyroid patients showed higher levels of alkaline phosphatase (ALP) and osteocalcin, and a higher urinary deoxypyridinoline/creatinine ratio, compared with controls (P <.05). In subclinical hyperthyroidism, only ALP was found to be higher compared with control values. No significant correlations were made in any group between serum IL-6 or TNF-a level and bone turnover markers. Results suggest that serum IL-6 level and markers of bone turnover rate seem to be increased in hyperthyroidism. This finding may support the role of IL-6 in induction of bone turnover in hyperthyroid states.