Rat sciatic motoneurones do not normally express NADPH diaphorase activity. However, after cutting the sciatic nerve in the mid-thigh of neonates and applying the retrograde tracer fast blue, such reactivity was found co-localized with fast blue in about one-fifth of sciatic motoneurones 4 days following the lesion. This proportion of sciatic motoneurones expressing NADPH diaphorase activity remained approximately constant for 14 days after axotomy during which time extensive motoneurone death occurred. Many NADPH diaphorase-positive motoneurones appeared shrunken with degenerative changes to the nucleus. In contrast, the same lesion in adult animals failed to induce any reactivity or cause motoneurone death 4–28 days after axotomy. Induction of nitric oxide synthesising capability may play a role in the death of target-deprived immature motoneurones.