Objective: To determine serum thiol/disulfide homeostasis in panic disorder (PD). Methods: Serum native thiol, total thiol, and disulfide levels were measured in the patients with 40 PD patients and 40 healthy subjects. Serum native thiol, total thiol, and disulfide levels were measured with a novel colorimetric, automated method. The thiol-disulfide ratio was also calculated. Results: The native thiol (p Conclusion: This is the first study in the literature to evaluate thiol-disulfide homeostasis in patients with PD. Our results suggest that the disulfide/thiol ratio is significantly greater in panic disorder patients.