YM348 is a potent and orally active 5-HT2C receptor agonist, which shows a high affinity for cloned human 5-HT2C receptor (Ki: 0.89 nM). YM348 has high affinity for cloned human 5-HT2C receptors with a Ki value of 0.89 nM and lower affinities for human-cloned 5-HT2B (Ki: 2.5 nM) and 5-HT2A receptors (Ki: 13 nM). To assess the binding specificity of YM348, a broad evaluation of an additional 46 binding sites including several other 5-HT receptor subtypes (1A, 1B, 1D, 3, 4, 5A, 6, 7) is performed. IC50 values of YM348 are found to be >1 μM for all of the binding sites except for the human 5-HT1A receptors (Ki: 130 nM), bovine 5-HT1D receptors (Ki: 481 nM), human 5-HT7 receptors (Ki: 177 nM), and human α2A receptors (Ki: 126 nM).YM348 exhibits a full-agonistic activity on human 5-HT2A and 5-HT2B receptors. The EC50 values of YM348 for 5-HT2C, 5-HT2A, and 5-HT2B receptors are 1.0, 93 and 3.2 nM, respectively. Oral administration of YM348 induces penile erections and hypolocomotion in rats, being completely inhibited by a selective 5-HT2C receptor antagonist, SB242084. YM348 inhibits spontaneous activity in a dose-dependent manner with a minimum effective dose of 0.203 mg/kg.