Nerve injury in neonatal rats leads to considerable motoneuron death. We investigated whether treatment with riluzole (a presynaptic inhibitor of glutamate release) is able to enhance survival of motor units (MUs) in the slow soleus (Sol) and fast extensor digitorum longus (EDL) muscles after sciatic nerve crush in newborn rats. Examination of 3- to 4-month-old rats revealed a beneficial effect of riluzole treatment after injury carried out on the first day after birth. At this time increased MU survival occurred in both the Sol and EDL muscles. In rats with nerve injury carried out on the second day after birth, increased MU survival occurred only in the Sol. We conclude that although riluzole treatment can rescue motoneurons destined to die and improve muscle performance, its beneficial effect is age-dependent, and the difference between the rescue of Sol and EDL MUs may be due to the slower maturation of motoneurons to soleus muscle. These findings have important implications regarding the motoneuron properties required for riluzole's beneficial effect.