The mechanisms of 12(S)-hydroperoxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid (12(S)-HPETE)-induced scratching were studied in ICR mice. In a recent paper, we demonstrated that the 12(S)-HPETE-induced scratching was reduced not by U75302 (BLT 1 receptor antagonist), but by LY255283 (BLT 2 receptor antagonist). In the present study, we tested various compounds to elucidate the mechanism of 12(S)-HPETE-induced scratching relating to transient receptor potential vanilloid type-1 (TRPV1), histamine receptor (H 1 ) and several serotonin receptors (5-HT 1 , 5-HT 2 , and 5-HT 3 ). As a result, 12(S)-HPETE-induced scratching was suppressed by capsaicin (TRPV1 receptor agonist), but not by capsazepine (TRPV1 receptor antagonist). Additionally, chlopheniramine (H 1 receptor antagonist) did not suppress 12(S)-HPETE-induced scratching, but cyproheptadine (H 1 receptor and serotonin 5-HT 2 receptor antagonist) potently suppressed the same response. Therefore, we tested several serotonin receptor antagonists to explain the detailed mechanisms relating to serotonin receptors. The scratching was reduced by WAY100635 (5-HT 1 receptor antagonist), or ketanserin (5-HT 2 receptor antagonist), but not by ondansetron (5-HT 3 receptor antagonist), after intradermal injection of 12(S)-HPETE. These results suggest that serotonin 5-HT 1/2 receptors are implicated in 12(S)-HPETE-induced scratching in ICR mice and that the TRPV1 receptor might not be directly related to 12(S)-HPETE-induced scratching.