Rat soleus muscle was partially denervated by resecting the L5 mixed nerve. Muscle reinnervation was monitored 10, 30 and 50 days after surgery. The extent of recovery was found to be dependent on the number of axons remaining in the muscle and appeared not to be influenced by the time allowed. If animals were treated daily with 5 mg/kg of gangliosides the enlargement of the motor units was further enforced. The index of sprouting (expressed as the ratio between the percentage of muscle reinnervation due to a certain number of motor neurons in reinnervation and in normal conditions) was increased in a significant way by gangliosides treatment, i.e. one motor unit can expand up to about 4.5-fold, but if the animal was treated with gangliosides the motor unit can expand up to about 6.3-fold. These results showed that motoneuron sprouting capacity is increased by treatment animals with gangliosides.