The anticonvulsant effect of 1-naphthylacetyl spermine (1-NA-Spm), an analogue of Joro spider toxin, against amygdaloid kindled seizures was studied in rats. 1-NA-Spm (10, 20 and 40 micrograms/rat) dose-dependently improved kindled seizures and shortened the afterdischarge duration 30 min after the administration. The anticonvulsant effect was observed even one day after the drug, and then gradually disappeared within 4 days. The present findings demonstrate that 1-NA-Spm acts as a potent and long-acting anticonvulsant against amygdaloid kindled seizures, and also suggest, together with the previous findings, that the calcium-permeable AMPA receptors, which are selectively antagonized by 1-NA-Spm, play a critical role in the seizure generation mechanism of amygdaloid kindling.