The purpose of this study was to investigate the association and dissociation kinetics of [3H]AT-1015 from 5-HT2 receptors in rabbit cerebral cortex membranes using a radioligand binding assay method and to make a comparison with those of [3H]ketanserin binding. Scatchard analysis of [3H]AT-1015 binding in rabbit cerebral cortex membranes indicated the existence of a single class of binding sites (dissociation constant, Kd = 2.18 nM). The specific binding of [3H]AT-1015 increased slowly with time and the association rate constant of [3H]AT-1015 binding (k1 = 0.1229 min-1 nM-1) was two times slower than that of [3H]ketanserin binding (k1 = 0.2451 min-1 nM-1). The dissociation rate constant of [3H]AT-1015 binding (t 1/2 = 37.03 min) was six times slower than that of [3H]ketanserin binding (t 1/2 = 6.29 min), when the addition of excess unlabelled ligands were AT-1015 and ketanserin, respectively. The dissociation rate constant of [3H]AT-1015 was slowed to a greater degree (t 1/2 = 163.40 min and t 1/2 = 198.12 min) by the addition of ketanserin and sarpogrelate as excess unlabelled ligands than was that of [3H]ketanserin (t 1/2 = 17.76 min and t 1/2 = 18.45 min) by the addition of AT-1015 and sarpogrelate as an excess unlabelled ligand, respectively. These findings on the dissociation kinetics of [3H]AT-1015 have confirmed and supported previously reported evidence of the slower dissociation of AT-1015 from 5-HT2 receptors.