In continuation of our work on the measurement of binding constants of organic substrates with Europium shift reagents, we have studied the steric effects of one or more alkyl groups on the binding of a series of eleven amines (anilines, pyridines and piperidines). Both steric and inductive parameters have proved to be important in determining binding constants for carbinols1, aromatic aldehydes and ketones2,3and esters3,4. The balance of these parameters is discussed for the amines and the results for the three anilines compared with figures derived by Infrared spectroscopy in an earlier study.