Cannulas were chronically implanted in the ventriculus lateralis of rats. The anticonvulsant effects of DN-1417 (γ-butyrolactone-γ-carbonyl-histidyl-prolinamide citrate) and TRH-T (pyroglutamyl-histidyl-prolinamide tartrate) were analyzed by observing the changes in convulsive threshold to electrical stimulation. Both DN-1417 and TRH-T had no significant effect on the electroconvulsive threshold. DN-1417 had an anticonvulsant effcet in animals pretreated with α-methylparatyrosine (α-MT). When rats were pretreated with FLA-63, a dopamine-β-hydroxylase inhibitor, the convulsive threshold was only slightly different from the control threshold, therefore, the decrease in the convulsive threshold by α-MT must be due primarily to a decrease in dopamine (DA) content. Changes in the DA content of the striatum also suggested that the anticonvulsant effect of DN-1417 was due to its DA releasing action. Furthermore, the anticonvulsant effect of DN-1417 seemed to have no relationship to the inhibitory activity of GABA.