Choline acetyltransferase activity was investigated in the superior cervical ganglia and in six microdissected regions of the medulla oblongata of the rat ipsilateral and contralateral to electrolytic lesions of the trigeminal sensory ganglia (Gasserian). Electrolytic lesions of the Gasserian ganglia failed to modify levels of enzymatic activity in all structures studied. This result would be an argument against the existence of a major cholinergic population of sensory neurones in the trigeminal system.