Previous studies from this laboratory have indicated that changing food availability of neonatal rats results in differences in functional development of the kidney. Results here show that during early development only, kidney to body weight ratios were lower for animals from reduced litters in comparison to those from Heart intact litters. In contrast, heart to body weight ratios were lower in animals from intact litters. In adult animals, no differences in organ weight to body weight ratios could be established between animals from different litters. It is suggested that these relationships are not determined by a common body weight factor like the amount of fat or change in muscle or skeletal mass which may however, account for the observations that animals from reduced litters are heavier than those from intact litters at a given age. It is argued that every organ studied reaches a maximum organ to body weight ratio sometime during development.