The effect of estrogen on the concentration of glycogen was determined in tissue samples from the uterus, liver, diaphragm and urinary bladder of spayed, alloxan-diabetic rats. Uterine glycogen was significantly increased in the alloxan-diabetic animals. Furthermore, uterine glycogen was significantly higher in the estrogen-treated alloxan-diabetic rats than it was after either alloxan treatment or estrogen treatment alone. These increases appeared to be related to the elevated blood sugar. The glycogen content of the urinary bladder was not altered.