The results are given on an investigation of the effect of 2 percent additions of nine aromatic amines on the knock-limited performance of AN-F-28 28-R aviation gasoline. The amines tested were aniline, technical pseudocumidine, p-toluidine, o-toluidine, m-toluidine, N-methylaniline, N-ethyl-p-toluidine, p-tert-butylaniline, and cumidines from synthetic cumene. The tests were performed on a CFR F-4 engine equipped with two independent fuel systems. Results showed that p-toluidine and p-tert-butylaniline gave the best over-all improvement in the knock-limited power of 28-R aviation gasoline at the three sets of engine conditions tested. Aromatic amines that might be of interest as antiknock agents are p-toluidine, p-tert-butylaniline, technical pseudocumidine, m-toluidine, N-methylaniline, and cumidines.