Previous studies suggested that an inverse relation existed between concentrations of body fat and muscle glycogen among inbred strains of mice. Of six strains, one, the I strain, was resistant to obesity, and the levels of muscle glycogen were 3–6 times greater than those of the other five strains. Because the tentative proposal was based on data from only one lean strain, mice of the DBA strain were studied as another possible lean strain. Although small animals, sublines 1 and 2 of this strain became obese when fed a 50% fat diet, and the levels of muscle glycogen were in the range of the other five obese strains. It was also found that concentrations of body fat up to 25% could be induced in 4–5-month-old mice of the I strain, and by dietary means alone. The concentrations of muscle glucogen in these mice were not lower than those of I strain mice exhibiting concentrations of body fat of 11%. It was concluded, therefore, that an inverse relation between carbohydrate and fat stores does not exist among inbred strains of mice. The unusually high levels of muscle glycogen in the I strain appear to be unique, and are most likely genetically determined.