Abstract— The ChAc activity of spinal and sympathetic ganglia was measured throughout the embryonic life of the chick.In spinal ganglia, the ChAc activity reached a first peak when the maximal proliferation of neuroblasts occurred. Then, the relative ChAc activity decreased. After the 12th day of incubation, the enzyme activity increased again and reached a second peak on the 16th day.In sympathetic ganglia, the general course of the development of ChAc activity was similar to spinal ganglia. However, higher enzymic activity was found. Furthermore, the earlier peak of ChAc activity occurred 48 hr later than the corresponding peak in spinal ganglia.The behaviour of ChAc activity in these two areas of the developing nervous system is interpreted as a function of their histogenesis.