Abstract THERE are probably few traits in the domestic fowl that have been given more attention by the biologist than the development and hatchability of the eggs. The reason for this is apparent in that few problems can be studied successfully unless a reasonable hatchability is maintained. The factors affecting the development and subsequent hatching of eggs are numerous, and such factors influence hatchability not only before the eggs are incubated but even before they are laid. Landauer (1941) has presented a resume of research on the hatchability of chicken eggs as influenced by environment and heredity. The present study is a report on hatchability as it occurred among 15 different inbred lines of chickens maintained at this Laboratory. MATERIALS AND METHODS The foundation birds used in this study were of the Single Comb White Leghorn breed and were obtained as hatching eggs from nine different breeders located in widely separated . . .