Several serotonergic drugs were tested in isolation-induced aggressive behavior in male mice using ethological methodology. Eltoprazine, a mixed 5-HT1 agonist, reduced aggression but enhanced social interest and exploration. Several 5-HT1A agonists (8-OH-DPAT, ipsapirone, buspirone, 5-Me-ODMT) and a 5-HT uptake blocker (fluvoxamine) also reduced aggression. Although these drugs somewhat differentially affect aggressive behavior, the isolation-induced paradigm alone is not sensitive enough to successfully differentiate and screen the various serotonergic drugs with regard to their influence on social behavior in mice. It is argued that various animal paradigms in several species are necessary to describe specific effects of serotonergic drugs.