An attempt has been made to study the influence of the acyl group in the N-chlorination of acylbenzylamines by chlorine. It has been proved (from both sides of the equilibrium) that the N-chlorination is reversible in acetic acid-water mixtures. Media of different acetic acid contents have been used to show that the N-chlorination reaction is complete up to 80% acetic acid, but that the equilibrium lies to the left in glacial acetic acid. The velocity of N-chlorination decreases with increase in the proportion of acetic acid in the medium. Chlorination in the nucleus is slow in all media, and is negligible in the time required for N-chlorination in 40% acetic acid. N-chloroacylbenzylamines undergo a low transformation, in presence of hydrogen chloride, to form nuclear chloro-derivatives. In 40% acetic acid, N-chlorination can be treated as an irreversible reaction. Concentrations of the reacting substances have been varied to prove that a second order equation is valid for the reaction. Rate a of N-chlorination have been measured for all compounds at 18oC, and for some compounds at 0oC, in order to measure activation energies. For N-chlorination of Ph.CH2.NH.CO.R the following rate sequence has been established: R = CH2.Cl < H < {CH3 < CH2~CH3CH2CH2 >(CH3)2CH > (CH3)3C} For N-chlorination of Ph.CH2.NH.CO.C6H4. x-p the following rate sequence has been established: X = NO2 C(CH3)3} . These results are compared with the results of previous work on the N-chlorination of acylanilines and they are discussed with reference to inductive effects, hyperconjunction and steric hindrance by alkyl groups. An attempt is made to interpret the Arrhenius parameters.