The riboflavin binding protein (RBP) content of individual egg components were followed through the development of fertilized eggs. Total proteins of the tissues were analyzed. The disappearance of RBP from the yolk and albumen occurred at the same rate as the total proteins. There was no evidence of any increase of free riboflavin nor degraded RBP in the yolk and albumen. Hence, it appears that the riboflavin was taken in by the embryo as the riboflavin-protein complex. The individual embryos showed some RBP accumulation through the first fourteen days of development. This may be an indication that the embryo is taking in the riboflavin-protein complex faster than riboflavin is utilized during the early stages of incubation. However, the beginning of a more rapid rate of growth at 13-14 days, was associated with the start of a gradual decline in the level of RBP in the embryo. This may suggest that the need for riboflavin exceeds the rate of transfer from the yolk and albumen reservoirs. RBP-riboflavin complex appears to be degraded after transfer to the embryo.