The combined use of di-n-propylacetate with phenazepam, diazepam, phenobarbital or phenytoin was shown to be followed by reciprocal potentiation of the anticonvulsant activity of the drugs in a variety of experimental epileptic seizures in mice according to the tests of shock and antagonism with corasole and thiosemicarbazide. The potentiating effect of the subthreshold dose of di-n-propylacetate on anticonvulsant effects of benzodiazepines, phenobarbital and phenytoin was more pronounced than the effect of the drugs administered in the subthreshold doses on the anticonvulsant activity of di-n-propylacetate. Of both combinations, di-n-propylacetate plus benzodiazepines proved to be most efficacious one. The unidirectional effect of the combined drugs on the different stages of the development of GABA-ergic system inhibitory function in the CNS activity is assumed to be of importance in the mechanism of reciprocal potentiation.