CILIARY neurotrophic factor (CNTF) supports the survival of embryonic motor neurons in vitro^1,2 and in vivo³, and prevents lesion-mediated degeneration of rat motor neurons during early post-natal stages⁴. Here we report that CNTF greatly reduces all the functional and morphological changes in pmn/pmn mice⁵, an autosomal recessive mutant leading to progressive caudo-cranial motor neuron degeneration. The first manifestations of progressive motor neuronopathy in homozygous pmn/pmn mice become apparent in the hind limbs at the end of the third post-natal week, and all the mice die up to 6 or 7 weeks after birth from respiratory paralysis. Treatment with CNTF prolongs survival and greatly improves motor function of these mice. Moreover, morphological manifestations, such as loss of motor axons in the phrenic nerve and degeneration of facial motor neurons, were greatly reduced by CNTF, although the treatment did not start until the first symptoms of the disease had already become apparent and substan-tial degenerative changes were already present. The protective and restorative effects of CNTF in this mouse mutant give new perspectives for the treatment of human degenerative motor neuron diseases with CNTF.