Intra-abdominal placement of the testes with vas deferens ligation decreased the contractile response to noradrenaline in the ipsilateral vas deferens without altering the contractile response to EFS and high K+. This difference could be caused by a reduction in the number of postjunctional alpha-adrenergic receptors or decreased receptor sensitivity. Both possibilities suggest that the vas deferens may initiate sympathetic activity, which may be responsible for contralateral testicular deterioration.