Abstract Background: Much interest has been drawn to the investigation of the hypothalamic–pituitary–thyroid (HPT)-axis in patients suffering from depression or panic disorder. However, there is no data concerning agoraphobia. Methods: Patients with panic disorder, agoraphobia, major depression were compared to normal controls (total n=88) in respect to HPT axis, obtaining basal TSH and administering a TRH test. Results: Normal controls and agoraphobics showed significantly higher Δ max TSH than depressives and panic patients. There were no differences between agoraphobics and normal controls. Conclusions: Agoraphobia, unlike depression or panic disorder, seems to be less biologically determined in respect to the HPT-axis.