A comprehensive investigation of the innervation of the vas deferens of the mouse was made using pharmacological, histochemical and electronmicroscopical techniques. 2. Guanethidine inhibited the response of the vas to transmural stimulation and potentiated the response to noradrenaline (NA). Phentolamine abolished responses to NA and to transmural stimulation. 3. After chemical sympathectomy degenerative changes were seen in presumptive noradrenergic axons; histochemical fluorescence due to catecholamines was absent. The vas failed to respond to transmural stimulation, and a 10-fold increase in sensitivity of the vas to exogenous NA was observed. 4. NA is shown to diffuse slowly through this tissue whose muscle cells are densely packed. This is disscussed in relation to the apparent "insensitivity" of the vas to exogenous NA. 5. A cholinergic component was identified histochemically which did not contribute significantly to the motor response of the vas as chemical sympathectomy abolished completely the motor response elicited by transmural stimulation. 6. It is concluded that NA is the motor trnasmitter for the smooth muscle of the vas deferens of the mouse.
