A new chicken ovalbumin phenotype which defect A1 band was found in a Hinaidori population in Japan.The relative concentrations (%) of A1, A2 and A3 bands of ovalbumin were 85:12:3 in normal, 0:93:7 in A1 defective type and 41:54:5 in heterozygotes.Mortality of embryos in A1 defective egg to 14 days of incubation was significantly higher than that in normal eggs. Hatchability of fertilized eggs from an A1 defective hen was very low (1.5%) compared to that of eggs from a normal hen (63.2%) in the same population.From these results, it was recognized that embryos from A1 defective ovalbumin hens experience high mortality.The symbol Ovc was used to designate the allele which causes the A1 defective ovalbumin.(Jpn. Poult. Sci., 34: 87-93, 1997)