Abstract— Choline acetyltransferase (ChAc) and acetylcholinesterase (AChE) levels were measured quantitatively in samples from the archi‐ and paleocerebellar vermis (Larsell's Lobules IX c,d,‐X, and Lobules VII‐VIII, respectively) and from the cerebellar peduncles, nuclei and white matter of rat and guinea pig. Lesions to isolate archi‐ or paleocerebellar areas were made in some rats and the effect on enzyme levels and ultrastructure were studied. In the rat there was a striking correlation between the activity of ChAc and AChE in the different areas; thus in the archicerebellar cortex the levels of both enzymes were 3–4 times those in the paleocortex. Deafferentation caused a fall in ChAc and this practically paralleled the fall in AChE in the same area. The reduction in both enzymes was more pronounced in the archi‐ than in the paleocerebellar cortex. In the guinea pig the results were very different. The ChAc activity was much lower than in the rat and was equal in the archi‐ and paleocerebellum. The AChE activity was also uniform in the different areas but, in contrast to ChAc, was higher than in the rat.