To investigate the changes during the differentiation of the cerebral neurons of chick embryo of tne embryogenic day (ED) 7 and 8, the ultrastructural changes in the cerebral neurons, the activity of dehydronases (LDH, MDH and SDH), protein expression profile and adenosine triphosphate concentration were analyzed. In ED 7 chick embryos, relatively large nucleus, centrally located nucleolus, evenly spread chromatin over nucleoplasm, and prominent nuclear envelope were observed. Oval-shaped mitochondria with well-developed cristae were present over entire cytoplasm. In ED 8 chick embryos, evenly spread chromatin over nucleoplasm, and prominent nuclear envelope were observed. In the cytoplasm, well-developed rough endoplasmic reticulum and Golgi complex were observed. In ED 7 chick embryos and ED 8 chick embryos, 31 polypeptide bands and 34 polypeptide bands were observed, respectively. The activities of dehydrogenases were lower in ED 7 chick embryos than in ED 8 chick embryos. LDH activity was 8.16 (ED 7) and 9.28 (ED 8), MDH activity was 7.98 (ED 7) and 10.10 (ED 8), and SDH activity was 5.49 (ED 7) and 7.14 (ED 8) respectively. The ATP concentration remained unchanged over ED 7 and 8.