Objectives: The present study was carried out to examine the thyroid diseases and major depression and to compare it with other psychiatric disorders. Method: The study was carried out with two groups of subjects, and experimental group, made up of 30 out-patients (15 male and 15 female) with major depressive disorder, and a comparison group made up of 30 out-patients (15 male and 15 female) with other psychiatric disorders. Thyroid tests, i. e. T4, T3RU, Base TSH, and TRH were administered to each patient. Findings: 30% of depressed patients and 36.7% of the subjects in the comparison group showed slow response to TRH. 13.3% of the depressed patients plus 16.7% of the comparison group showed an increased response to TRH. A t-test was applied, and no significant difference was noticed in the results of thyroid tests and of the TRH between the two groups. The interactive impact of sex and age on thyroid disease was studied in both groups. The hypothesis relating to the changes of TRH on depression are later discussed in the paper.