Protein kinase C (PKC) and growth-associated protein-43 (GAP-43) were investigated immunohistochemically in the dorsal motor nucleus of the vagus nerve and the hypoglossal nucleus after axotomy using monoclonal antibodies against type I, II and III PKC and GAP-43. In the control side of both nuclei, anti-type I and II PKC weakly stained neuronal cell bodies, while anti-type III PKC did not show any reaction with neurons. In the axotomized side of both nuclei, anti-type II PKC antibody intensely stained affected nerve cell bodies as well as plasma membrane. Some of the severed neurons showed intensified reactions for both anti-type II PKC and anti-GAP-43 antibodies in the serial sections. These findings suggest that axotomy increases the type II PKC of the severed neurons, and type II PKC seems to phosphorylate some protein, such as GAP-43, and plays some role in the retrograde neuronal reaction.