Our work in this area has been extended to the asymmetric synthesis of ditertiary arsines. Thus, the bis(aR)-phosphepine-stabilised diarsenium salt has been reacted at low temperature with n-butyllithium to give the (S,S)-bis(n-butylphenyl)diarsine in 88% enantioselectivity, along with 15% of the achiral (R,S) compound. The enantioselectivity of the reaction was determined by a novel NMR spectroscopic method involving the use of an enantiomerically pure diphosphineplatinum(II) group as the reference agent. This is the first asymmetric synthesis of a ditertiary arsine containing two chiral arsenic stereocentres.