The aim of this study was to evaluate the effect on the activity of the hypothalamic-pituitary dopaminergic system of two new atypical antipsychotic drugs: the ergoline derivative SDZ HDC-912, which is a dopamine (DA) D2 receptor partial agonist; and the quinolinone derivative OPC-4392, which acts as an agonist at presynaptic DA autoreceptors and as an antagonist at post-synaptic D2 receptors. The effects of both compounds were compared to the effects of the benzamide derivative amisulpride. Prolactin (PRL) and growth hormone (GH) levels before and after challenge with apomorphine (Apo), a dopaminergic agonist, were determined after at least 2 weeks washout and again after 1 month of treatment in DSM-III-R schizophrenic inpatients. SDZ HDC-912 significantly decreased Apo-induced PRL inhibition, and tended to decrease PRL secretion and Apo-induced GH stimulation. OPC-4392 induced a significant decrease in baseline PRL and in Apo-induced PRL suppression, and a non-significant decrease in Apo-induced GH stimulation. The neuroendocrine profiles of these two compounds agree with their dopaminergic properties; however, the decrease in PRL basal level differentiates the two drugs from neuroleptic agents.