Several neurochemical correlates of suicide were recently detected. Some authors found increased disorders in the hypothalamic-pituitary-adrenal (HPA) and -thyroid (HPT) axes and disturbances in serotonergic neurotransmission in suicidal patients. In order to investigate the biological correlates of suicidal ideation, we measured the following: basal thyrotropin-secreting hormone (TSH), free thyroxine (FT4), pre- and postdexamethasone cortisol, adrenocorticotropic hormone (ACTH) levels, the circulating concentrations of total L-tryptophan (L-TRP) and the ratio between L-TRP and competing amino acids (CAA). The subjects were 17 suicidal and 17 nonsuicidal major depressed females matched for age and severity of illness. We found no significant differences in any of the above-mentioned biological data between patients with suicidal ideation and those without.