A history of thyroid dysfunction has been reported in patients with phobic disorders. There is also evidence of a blunted TSH response to TRH stimulation in patients with panic disorder. In this study, values of T3, T4 and T7 were compared between 26 patients with panic attacks and 20 normal controls. Patients were diagnosed according to DSM-III criteria and those with a clinical history of thyroid dysfunction were excluded. Patients were not on any medication when the blood samples were drawn. The mean values of T3, T4 and T7 did not significantly differ between the two groups, suggesting no evidence of hypo or hyperthyroidism; however, the variance of distribution of T3, T4 and T7 values was significantly different between the two groups (Fmax values for T3: 2.55, p value less than 0.05; T4: 3.15, p value less than 0.01; T7: 2.55, p value less than 0.05).