Abnormal development in Bh quail embryos was histologically examined. In addition to the abnormal plumage pigmentation in Bh-heterozygotes and homozygotes, and subcutaneous hemorrhage and liver degeneration in homozygotes as previously reported, the lungs in all 10-day homozygotes examined showed hemorrhage, suggesting that the Bh gene may also be expressed in this organ. Other organs, including the esophagus, the gizzard, the small intestine, the large intestine, the pancreas, the metanephros, the heart, the gonads and the hemopoietic organs in heterozygotes and homozygotes were histologically normal on days 7 and 10, though the development of homozygotes was slightly delayed. Primordial germ cells and hemopoietic cells were normally developed in gonads and hemopoietic organs such as the bursa of Fabricius and the spleen of the homozygote, respectively. These results suggest that Bh is a mutation inducing pleiotropic effects such as plumage pigmentation changes in both heterozygotes and homozygotes, and abnormal development of the blood vessels in the skin, the feather germs and the lung in homozygotes.