It is well established that treatment of rodents with 'glucocorticoids' inhibits growth. This was originally thought to be a toxic effect (Ershoff, 1951). With the acceptance of the concepts of Selye (1960), according to which the stimulation of corticosteroid secretion in response to various environmental stresses is a factor leading to a shortened life-span, the observations that adrenocortical steroids inhibit growth strengthened the view that an excess of these compounds was toxic. However, it is known that, in some circumstances, rats injected with corticosteroids maintain good health for a considerable period of time (Silber & Porter, 1953), in spite of a greatly reduced growth rate. Since the metabolic characteristics of these animals are similar to those of undernutrition, the interpretation of biochemical changes requires a knowledge of the time course of both growth and food intake. Because of the confusion which surrounds this issue it was decided to measure weight