Three epimeric mixtures of trinorbornylboranes have been prepared, in which the percentages of exo- and endo-norbornyl groups are 99·2 and 0·8%, 66 and 34%, and 14 and 86%, respectively. All three react with oxygen to give norbornylbis(norbornylperoxy)borane containing about 76%exo- and 24%endo-norbornyl–oxygen links, and the reactions are inhibited by galvinoxyl, copper NN-dibutyldithiocarbamate, and phenothiazine. It is proposed that the autoxidations follow a homolytic chain mechanism involving a common norbornyl radical.