Using the model of agonistic behviour in mice we evaluated the effect of the selective 5-HT1A receptor ligand S 15535 on paired social interactions of singly-housed male mice with non-aggressive group-housed partners. The study brought the evidence that S 15535 possesses marked antiaggressive effect and less pronounced anxiolytic activity, results resembling those of our earlier testing of other selective 5-HT1A ligands flesinoxane and buspirone.