The reactions of trimethylgallium and trimethylindium with a variety of secondary amines [HNMe2, HNEt2, HNPr2n, HNPr2i, HNBu2i, HNBu2s, HN(CH2Ph)2, HN(c-C6H11)2, HNC4H8, HNC5H10, HNC6H12 and HN(CH2CH2)2NMe], produce a series of room-temperature stable liquid or solid adducts. These were characterized by 1H and 13C NMR, IR, mass spectrometry and elemental analysis. Spectroscopic comparisons are made between these and the corresponding trimethylaluminum derivatives. 1H and 13C NMR data for all three series of adducts indicate a correlation between the chemical shifts of the methyl groups on the metal and the relative steric requirements of the amines. The data show a general downfield movement of these chemical shifts with increasing steric bulk. © 1995.