THE purpose of this work was to compare the seizure thresholds of two genetically different strains of rats. Rosenzweig, Krech and Bennett1 have shown that the descendants of Tryon's2 maze brights (S1's) are superior in learning ability to the descendants of Tryon's maze dulls (S3's) and that the S1's have higher levels of cerebral cortical acetylcholine and cholinesterase activity. These workers believe that the S1's nervous transmission is more efficient and propose this as part of the reason for the superior learning ability of the S1's.