In order to clarify the metabolism of protein and carbohydrate in chick embryos, changes in body and liver weights, total serum protein levels, and liver glutamic-oxalacetic transaminase (GOT) activities were examined in 8-day-old and older chicken embryos and 1-day-old chicks of White Leghorn, Rhode Island Red and their reciprocal crossbreds, and Hinaidori. Total serum protein levels were measured by the method of LOWRY et al. (1951) and the GOT activities by the method of REITMAN-FRANKEL (1957). To reveal the existence of isozyme and its cellular distribution of GOT in embryonic liver, the starch gel electrophoresis described by LUSH (1961) and the fractionation of liver tissue used by ODA (1973) were employed. The following results were obtained:<br>1. Body and liver weights increased progressively with the development of embryos. Growth of embryo at the early stage was particulary rapid in Hinaidori, and the ratio of liver weights to body weights in this breed was higher than that in other breeds. In crossbreds, growth curves were similar to those of their maternal breeds.<br>2. Total serum protein levels increased gradually with the development of embryos in each breed and crossbreds except for Hinaidori, although they decreased temporarily at a period before hatching. In Hinaidori, after the level reached a peak in 16-day-old embryos, it decreased and showed the lowest at hatching time of all breeds.<br>3. The liver GOT activities were high at the middle stages of embryonic development in each breed, but the stages at which the highest activity occurred varied between breeds or crossbreds. In Hinaidori, the stage showing the highest level was retarded but the level of GOT activities in this breed was higher than in any other breed. In both crossbreds, the level of GOT activities was higher than in their parent breeds.<br>4. GOT isozymes were detected in the liver by means of starch gel electrophoresis. Namely, there were four bands, consisted of three bands migrated towards the anodal end and a band migrated towards the catholic end. By cellular fractionation, it was recognized that the GOT isozymes in the soluble fraction correspond to the bands migrated towards the anodal end, and that of the mitochondrial fraction correspond to the band migrated towards the cathodic end. High activities of GOT were observed in the soluble fraction.