Aryl amine reaots with formaldehyde and benzoimidazole in ethyl alcohol to give arylamine-benzoimidazole N-Mannich base in good yield.Seventeen suoh bases,of which eight are new oompounds,were prepared by this method.Arylamine-benzoimidazole N-Mannioh bases undergo egohange reaotions with aoetophenone in the same manner as the N-Man.nich bases from arylamines,formaldehyde and sucoinimide.These results provide a new method for preparing arylaminopropiophenones.It is proposed that the egohange reaotion probably proceeds by an elimination-addition mechanism.