Adducts of trichloro and triisothiocyanato borane with alkyldimethylamines are effective latent catalysts for epoxy homopolymerization. The lower stability triisothiocyanato borane adducts initiated the polymerization at lower temperatures than the chloro derivatives. In both cases the borane moiety was converted into [B(OR)(4)](-) by reaction with the oxirane ring initiating the reaction by the formation of cations. Free amine was detected in the curing resin but was not directly involved in the polymerization mechanism. The formation of oxazolidone rings was observed when triisothiocyanato borane adducts were used. The behaviour of some of the decomposition products of the adducts was also examined.