Several neuroendocrine studies with the clonidine-growth hormone stimulation test show endogenous depressive patients to have a reduced GH response as compared to neurotic depressives, schizophrenics and controls. The blunted GH response to clonidine seems to be a trait marker or vulnerability factor for mono- and bipolar endogenous depression. It could be explained by a reduced postsynaptic α2-adrenoceptor sensitivity or of structures related to them. The sensitivity of α2-adrenoceptors is influenced by both, the endorphinergic and cholinergic systems. First results supporting this concept are presented and discussed.