This study investigated the effects of a short period of severe protein malnutrition on subsequent growth and development in the squirrel monkey. A total of 12 newborn monkeys were fed a low protein diet from 2 to 8 weeks of age then rehabilitated by returning them to the 13 percent protein diet of the control group. Minimum amount of protein needed for maximum growth was about half that of the control diet. For one year, measures of body weight, plasma protein and albumin concentration, hemoglobin and locomotion were collected for protein deficient and control animals. Results, which show lasting effects of body weight deficit and markedly depressed plasma albumin levels during the malnutrition, attest to the severity of protein malnutrition induced in these animals. Autopsy data obtained from animals who died during the period of the malnutrition indicate that brain weights were depressed and that malnutrition interfered with brain development. (GO)