The rate of regeneration and the initial delay of the fastest growing fibers of the rat sciatic nerve were electrophysiologically evaluated after a freeze at mid-thigh. A prior section or a prior freeze at the ankle level increased the rate of regeneration and decreased the initial delay with different magnitudes. These phenomena are named 'conditioning lesion effects'. A daily electrical stimulation transcutaneously delivered to the foot sole muscles from the day following their denervation by the prior lesion did not modify the increased rate of regeneration but prevented the decrease of the initial delay whatever the type of the prior lesion. Therefore, the initiation of earlier sprouting of the parent axons seems to be specifically controlled by a signal associated with muscle denervation properties.