BCL-XL and Bcl-2 proteins were identified by paraffin section immunohistochemistry in the neuropil core of the barrelettes of the caudalis spinal trigeminal nucleus 6 h after birth. They were subsequently identified at progressively more rostral levels of the trigeminal pathway, peaking in barreloid neuropil cores in the ventral posterior thalamic nucleus at postnatal day (P)4.5, and in cortical barrel cores at P7. Labelling was confined to the cores of barrel-like structures surrounded by immunonegative shells and became progressively less distinct at all levels from P8. These protein products, which are usually considered to control the onset of apoptosis, may serve other functions in the axon terminal fields of the trigeminal pathway.