The autoxidation of butylboranes and related compounds are considered and the evidence favouring a free-radical chain mechanism is described. Analogies with hydrocarbon autoxidations were observed particularly towards antioxidants known to react with peroxy-radicals. Inhibition by galvinoxyl gives some information about the easy initiation step. The rapid propagation step was affected by nitroxide radicals and a nitroxide–alkyl radical adduct was isolated. (+)-Di-isopinocampheyl-s-butylborane was comparatively stable in contact with diborane and autoxidised with extensive racemisation of the butyl group.