Rates of total body protein turnover during growth greatly exceed those necessary for net protein deposition. The excess protein synthesis would appear to be energy wasteful. However, a constant relationship is noted between whole body protein synthesis and basal energy needs, except during periods of rapid growth and development (newborn and adolescence). We suggest that whole body protein turnover is regulated by basal energy needs. The excess synthesis seen during periods of rapid growth is probably necessary to permit development and remodelling of tissues and organs to take place coincident with a mere increase in size.