A model is developed which demonstrates the pattern of the relationship between growth rate. body weight, proportion of adult weight attained, and time taken to mature in animals. The relationships of growth rate and time taken to mature, to body weight in primates are examined in relation to this model. Within each of the taxonomic groups: prosimians, New World monkeys, Old World monkeys and great apes, growth rate quite closely parallels the three-quarter power of weight. After accounting for size, growth rate clearly decreases through this taxonomic list. Man has the slowest growth rate of all primates in relation to his size. The model predicts that, after accounting for differences in size, the daily energy intake during growth may, like growth rate, decrease considerably through the taxonomic groups from prosimians to man. The results form a basis from which to account for the differences due to size and taxonomic position when using monkeys as models for human physiology or disease during growth.