Pulse wave transmission rate has been measured "in vivo" in 6 male anaesthetized Wistar rats, by means of cannulae, inserted both in carotid and femoral arteries. The measure has been done by calculating the time delay of several corresponding levels in the two pressure pulses: at the foot, during the ascending phase, at the peak. Three different intervention have been carried out: Ach, NA, blood transfusion. The transmission rate outcame higher at the pulse foot than at the peak, in control animals and in Ach and blood transfusion interventions. The NA intervention inverted this behaviour, where the increase in transmission rate did not correspond to the rate of pressure growing. The possible influences of a vegetative component on arterial viscoelastic behaviour are discussed.