The administration to mice of crude substance P prepared from bovine brain inhibited strychnine convulsions. After alumina column chromatography, this antistrychnine activity was observed mainly in the fraction which was not adsorbed, while those fractions containing substance P or its satellite polypeptides (Zetler, 1963) were found ineffective. The regional distribution of such an antistrychnine activity in bovine brain was also found to be different from that of substance P. Experiments in which inactivation with proteases and dialysis were investigated suggested that the component or components bearing the antistrychine activity were of a polypeptide nature.