Rats fed on milk, Cu, and Fe reproduce for as long as 2 yrs. While 2d generation rats on this diet alone do not reproduce, the addition of the Daniels and Hutton salt mixture has a favorable effect on reproduction in the 2d generation, and addition of MnSO4 or of Mn and Si or of Mn and Al to a diet of milk, Cu, and Fe makes reproduction possible in the 2d generation. The 5th generation on milk, Cu, and Fe plus the Daniels and Hut-ton salt mixture is sterile. Addition of sucrose to milk, Fe, and Cu gives results poorer than on milk, Fe, and Cu alone.