Growth hormone release in response to all known stimuli of GH secretion is blunted in obese subjects. Several studies, using d,l-fenfluramine (d,l-FF) as a serotoninergic tool, suggest that brain serotonin plays a role in the pathogenesis of this phenomenon. However, the effect of d,l-FF appears to be dependent on the stimulus used to induce GH release. Furthermore, d,l-FF has catecholamingergic properties apart from its capacity to stimulate serotonin release and to block its re-uptake. In this study, we investigated whether subchronic treatment with the highly selective serotoninergic drug dexfenfluramine (d-FF) affects the GH response to galanin or GHRH in obese subjects.