Brain serotonin plays a crucial role in the regulation of food intake and body weight homeostasis. Previous data suggest an interaction with corticotropin-releasing hormone (CRH). To further examine the interaction between these neurotransmitters, the selective serotonin reuptake-inhibitor (SSRI) fluvoxamine was given intraperitoneally in fa/fa Zucker rats with and without the CRH-receptor-antagonist alpha-helical CRH administered intracerebroventricularly (i.c.v.). The saline treated animals gained weight. Fluvoxamine led to a significant weight loss while not affecting food intake. Furthermore, insulin levels in this animal model were reduced following fluvoxamine administration. These effects were antagonized by alpha-helical CRH and are thus most likely mediated via CRH or CRH-like peptides.