Apoptosis, programmed cell death, is a regulating mechanism enabling the removal of superabundantly produced and unnecessary cells. Disturbances of the apoptosis regulation contribute to the pathogenesis of many diseases, including Hashimoto's thyroiditis (HT). Objective: To assess levels of antiapopototic proteins; soluble Fas (sFas) and soluble Bcl-2 (sBcl-2) in sera from patients with HT,evaluate their relationship to antithyroperoxidase antibodies (TPO Ab) and their significance as markers of disease activity. Subjects and Methods: Sera concentration of sFas and sBcl-2 were assayed by Enzyme Linked Immunosorbent Assay (ELISA) in 32 patients with HT (19 with untreated HT, 13 with euthyroid HT) and 15 age-matched healthy adults as a control group. Results: sFas levels were significantly higher in both untreated HT patients (6960±1542 pg/ml) and euthyroid HT patients (6160±1397 pg/mL) compared to controls (5280±938 pg/ml), with p values were