The products of the pyrolysis of mixtures of diborane with amines have been isolated and characterized in argon matrices at 14 K. For all three methylamines, the 1/1 adduct H3B.NH(x)(CH3)y (x + y = 3) was isolated. In addition, the H-2-elimination product was isolated when mono- or dimethylamine was employed. H2B = N(CH3)2 was identified by comparison of its spectrum with literature spectra, while monomeric H2B = N(H)CH3 was isolated for the first time and characterized spectroscopically. Further information concerning the B-N stretching frequencies of, and the bonding in, these species was obtained. The mechanism of formation of these products from the precursors is also discussed.