We measured serum thyroid hormone levels, and pre- and post-TRH administration serum thyrotropin (TSH) in 46 psychiatric inpatients with major depression (n = 20), anxiety disorder (n = 9), and anxious depression (n = 17), and in 56 healthy subjects. Basal serum triiodothyronine was lower in female patients with major depression and anxious depression than in healthy women (P less than 0.05). Basal serum thyroxine was lower in female patients with anxious depression than in controls; all patients showed lower basal serum TSH than controls. In healthy subjects, basal triiodothyronine and thyroxine, basal TSH, and delta TSH (the increment of TSH after TRH administration) correlated, whereas no correlation was found between triiodothyronine and thyroxine in male patients with major depression, or between TSH and delta TSH in female patients with major depression or anxious depression. In female patients, 45% with major depression, 25% with anxiety disorder, and 35% with anxious depression showed a blunted TSH response. We also investigated pre- and post-dexamethasone administration cortisol levels in these patients. The sensitivity obtained by the combination of the results of the TRH and dexamethasone suppression tests for major depression, anxiety disorder, and anxious depression was 45%, 55%, and 65%, respectively.