Nucleolo-cytoplasmic relationships have been studied using histochemical techniques in the spinal cord of healthy neonates compared with those born to mothers malnourished through most of the gestation period, and healthy and severely protein-malnourished young adult squirrel monkeys. Formaldehyde-fixed as well as fresh frozen tissues were used for histological study and for histochemical techniques to demonstrate lipids, carbohydrates, nucleic acids and enzymes of various metabolic cycles. Changes in the neuronal cytoplasm of the low protein animals appear to be related to impaired protein metabolism and energy transport. The nucleolus reacts to cytoplasmic changes by enlarging its size and by active synthesis of secretion of nucleolar material, which is then passed into the cytoplasm through an evagination of the nuclear envelope. The greater the degree of chromatolysis in the cytoplasm, the more active the nucleolus appears to be in terms of its enlarged size and transfer of secretion products into the cytoplasm. It is believed that the perinuclear accumulation of secretion products in the neuronal cytoplasm of the protein-deficient animals has its origin in the nucleolus. Such an accumulation in the severely malnourished animals appears to be a compensatory mechanism for the increased cytoplasmic 0 catabolism and loss of ribonucleoprotein material in order to facilitate additional protein synthesis for cell survival.