Infant rhesus monkeys were fed either a control, dilute or low protein diet from 1 to 7 months of age, and the control diet from age 7 to 12 months. All diets were fed ad libitum. Curves were fitted for energy and protein consumption and for growth in weight, length and head circumference. Both experimental groups developed increasing deficits of energy and protein consumption during the undernutrition experiment. With nutritional rehabilitation, the animals previously fed the dilute diet immediately increased their consumption of energy and protein to levels appropriate for age. Those previously fed the low protein diet showed an increased nutrient uptake, but one more appropriate for size peers. Reduced growth velocity occurred with both experimental diets. "Catch-up" growth, and growth velocity per unit diet energy and protein was most obvious for body weight, but recovery from growth deficits was most complete for growth in head circumference. Nutrient deficits accumulated by animals fed the dilute diet were not recovered during catch-up growth; catch-up growth occurred in animals previously fed the low protein diet even though cumulative nutrient deficits were increasing.