The pattern of expression of p75, the low affinity nerve growth factor receptor, in the adult rat cerebellum and its fate after a traumatic lesion were analysed using immunohistochemical localization of this receptor. A subset of Purkinje cells was immunoreactive for low affinity nerve growth factor receptor in the intact adult cerebellum. These cells were arranged in alternating positive and negative parasagittal compartments along the cerebellar cortex. This pattern of expression had 90% homology with zebrin I. After a traumatic lesion, the specific pattern of expression of zebrin I remained unchanged, whereas the low affinity nerve growth factor receptor pattern changed as early as one day: Purkinje cells near the lesion site, independent of zebrin I staining, became immunoreactive. During the first week, the increase in immunoreactivity remained high. Thereafter, there was a short, fast decrease followed by a long period in which a faint immunostaining on lesioned Purkinje cells is maintained for up to one year. The increase in the expression of the low affinity nerve growth factor receptor by all traumatically affected Purkinje cells suggests a correlation between this specific up-regulation and the high resistance of these neurons to axotomy or other traumatic injuries.