A thorough study of the reactions of phosphino- and arsino-potassium with silyl halides in dimethyl ether at low temperatures has enabled effective syntheses of the silyl phosphines and arsines to be devised, and provides evidence for the existence of stable salts of the type KP(SiH3)2. Disilylarsine has been prepared by the analogous reaction of lithium tetra-arsinoaluminate, LiAl(AsH2)4.