Female chickens were fed graded levels of sodium selenite to determine at what level a selenium toxicity occurred. In the first experiment a basal diet was supplemented with 0, 0.1, 1.0, 3.0, and 5.0 ppm of selenium. These levels had no effect on egg production, egg weight or fertility of the eggs. Hatchability of fertile eggs was significantly decreased by 5 ppm of dietary selenium. In the second experiment a basal diet was supplemented with 0, 5.0, 7.0, and 9.0 ppm of selenium. Egg weight and hatchability were significantly decreased by 7 and 9 ppm, and egg production was decreased by 9 ppm of selenium in the diet. When selenite was added to the diet, there was a lag of 2 to 3 weeks before the selenium content of the egg reflected the content of the diet. As long as the selenium content of the diet remained the same, egg selenium remained the same. When selenium was no longer supplemented, egg selenium content decreased. Two weeks after cessation of selenite supplementation, egg selenium was markedly reduced. Four weeks after cessation of selenite supplementation, egg selenium levels approached those of birds fed a basal diet continuously.