The preparation of various complexes of diethylaluminium halides with ligand molecules is described. The complexes obtained were of the 1 : 1 type except for the iodo-pyridine derivative which has 1 : 2 stoicheiometry (C2H5)2AlI,2C5H5N. The proton nuclear magnetic resonance (n.m.r.) spectra of the various compounds are discussed, and a relative order of the acceptor strength of the halides is deduced.