Chronic administration of methamphetamine (METH) elicits progressive enhancement of locomotor activity known as behavioral sensitization. We have recently shown that chronic METH enhanced METH challenge-induced increase in 5-HT levels in the prefrontal cortex and that 5-HT(1A) receptor activation attenuated this neurochemical sensitization as well as behavioral sensitization. This study examined whether the nonselective 5-HT(2) receptor antagonist, ritanserin affects METH-induced behavioral and neurochemical sensitization in mice. Ritanserin at doses of 1 and 3 mg/kg inhibited the development and expression of METH-induced behavioral sensitization in a dose-dependent manner. Furthermore, chronic administration of ritanserin for a week attenuated the maintenance of behavioral sensitization, indicating the improvement of established behavioral sensitization. Microdialysis analysis showed that chronic ritanserin inhibited the neurochemical sensitization that chronic METH enhanced METH challenge-induced increase in extracellular 5-HT levels in the prefrontal cortex. Furthermore, acute ritanserin inhibited METH challenge-induced increase in extracellular 5-HT but not DA levels in the prefrontal cortex. These results suggest that 5-HT(2) receptors are involved in METH-induced hyperactivity and behavioral sensitization in mice.