When Knorr-Paal condensation is to be employed in synthetic work, the experimental conditions must be designed according to the two feasible reaction pathways and four possible catalytic conditions which we have so far discovered in mechanism studies. For the condensation with strongly nudeophilie amine no catalyst or only basic catalyst should be used while for that with weakly nucleophilic amince ox with one of considerable steric resistance an acid catalyst ought to be applied.