The influence of stresses of various etiology (prolonged isolation, inescapable electrostimulation) on the antiaggressive effect of anxiolytics was studied in outbread white male rats. It was established that, in contrast to the anticonflict effect (decreasing under the action of stress), then antiaggressive action of the drugs studied (diazepam, phenazepam, clonazepam, alprazolam) exhibits qualitative changes. In the absence of stress, the threshold of aggressive reaction is low and anxiolytics increase this level. Under the action of stress, the threshold of aggressive reaction increases, and the same drugs reduce this threshold to the normal level, thus producing proaggressive action. The degree of changes and the rate of restoration of the initial activity depend on the efficacy of anxiolytics, the strength and duration of stress, and on the duration of drug administration during the stress aftereffect. A possible mechanism of this phenomenon can be the interaction of the GABA-benzodiazepine and opiate endogenous systems.