Anionic process for the polymerization of lactam

A process for polymerizing .omega.-lactams to high molecular weight polyamides by heating a mixture of at least one kind of .omega.-lactam, an anionic catalyst comprising the reaction product of a strong base and an .omega.-lactam, and an N-substituted ethyleneimine derivative of the general formula ##EQU6## wherein n is 2 or 3 and R represents a divalent or trivalent organic group which has no active hydrogen with an activity higher than the hydrogen of >N--H of the lactam to be polymerized, said N-substituted ethyleneimine derivative being present in an amount of from about 0.01 to about 5.0 mol percent to the amount of said .omega.-lactam to be polymerized.