Yohimbine treatment inhibited isolation-induced attack in mice but had no effect on defense. The drug also increased social distances and produced a transient decrease in preference for conspecific male odors. The antiaggressive actions of yohimbine parallel those reported for the anxiogenic beta-carbolines and for phenylpiperazine "serenic" agents. The results emphasize the importance of supplementing conspecific agonistic encounters with additional behavioral measures such as nonagonistic social attraction in evaluating antiaggressive drugs. The decreased responsiveness to conspecific odors seen in Experiment 3 also suggests that increased conspecific avoidance may be mediated, in part at least, by altered olfactory processes.