Summary and ConclusionsTotal body water by vacuum desiccation, total body fat by ether extraction, and fat-free dry body weight were measured in normal mice and rats, and in starved and dehydrated rats. In normal animals total body water was not shown to differ from a direct proportion of fat-free dry weight, and body fat was not shown to have an independent effect on total body water. On the other hand, severe dehydration reduced total body water expressed as percent of fat-free body weight in adult female rats from 72.2 to 67.5. Mice and weanling rats had total body water of 74.0 and 74.7%, respectively, of the fat-free body weight, significantly more than did normal adult rats.