Nerve growth factor (NGF) promotes the survival of several neuronal populations, but recently it has also been shown to induce neuronal cell death. Here we report the effects of NGF on lesioned motoneurons. We have analyzed facial and sciatic motoneurons in newborn and adult BALB/c and C57BL/6 mice, in addition to mice deficient in the low-affinity p75 receptor for the neurotrophins (p75NTR). NGF application did not alter survival of lesioned facial motoneurons in any of the strains examined independent of the age of the animals. Only in the adult C57BL/6 mouse strain where the sciatic nerve had been crushed prior to factor application did NGF induce cell death of axotomized sciatic motoneurons. Our results illustrate the importance of the genetic background and the motoneuron sub-type in studies related to cell death and survival of motoneurons in relation to NGF and p75NTR.