Urinary pH was evaluated in panic disorder (PD) patients compared with both psychiatric and healthy control subjects. Fourteen PD patients, eight major depressive disorder (MDD) patients, and 14 healthy control (HC) subjects were examined. All patients were drug-free and met DSM-IV diagnostic criteria. The PD patients had lower urinary pH and higher levels of anxiety than both MDD and HC subjects. Additionally, urinary pH inversely correlated with anxiety levels. Although preliminary, these findings suggest that PD patients have lower urinary pH than MDD and HC subjects. Future studies that simultaneously examine both urinary and blood pH in larger numbers of PD patients and patients with other anxiety disorders, before and after treatment, need to be conducted.