Significant antidepressant effects have been reported after administration of dexamethasone and thyrotropin-releasing hormone (TRH). The purpose of this study was to evaluate whether or not the administration of the dexamethasone suppression test (DST) and TRH test in depressed patients, just before their entering clinical trials, has any impact on their symptoms. The Hamilton Rating Scale for Depression was administered to 166 subjects at screen visit, 1 week later (baseline visit), and 1 week after beginning treatment with fluoxetine 20 mg/day (week-1). Between screen and baseline visits, 62 patients were administered the DST alone, 6 underwent the TRH test alone, and 26 received both the DST and the TRH test. Seventy-two patients were not administered either test. No statistically significant differences in depression scores were found at screen, baseline and week-1 visits between patients who underwent neuroendocrine tests and those who did not. Our data suggest that the administration of neuroendocrine tests such as the DST and the TRH test does not have a statistically significant effect on depressive symptoms and, therefore, does not interfere with study results and interpretation.