2-pyrrolidones are prepared by hydrogenating a succinonitrile in the liquid phase in the presence of ammonia by passing an ammoniacal solution of a succinonitrile over a fixed bed catalyst, particularly of the trickle-phase type, in which the catalyst is nickel on an alkaline support such as calcium hydroxide or calcium carbonate. Attractive yields are achieved without the expense of filtering off and separating used catalyst as in prior procedures.