Female Holtzman rats, weighing about 40 g, were given one of each of the following treatments: (a) 6% protein diet ad libitum throughout; (b) 6% protein diet for 2 weeks followed by 25% protein diet ad libitum for 2 weeks; (c) 25% protein diet fed in amounts isocaloric with treatment (a) and (d) 25% protein diet ad libitum throughout. These treatments were applied from weaning (21 days) to 49 days of age. Selected pairs of treatments were compared in order to elicit the influences of protein-calorie malnutrition, malnutrition recuperation, and protein deficit on both the absolute and relative weights of the following head components: skin (plus subcutaneous adipose tissue), muscular mass, eyeballs, skull, and encephalon. DNA and total protein concentrations in encephalon and muscle were also measured. The head components were classified into stables, for which growth decreased less than that of the head as a whole, and variables, for which growth decreased more than that of the head as a whole. The eyeballs, encephalon, and skull behaved as stable components, whereas the muscular mass and skin did so as variable components. The well-known modifications in the craniofacial growth pattern evoked by nutritional deficiencies were explained by the different reactions shown by the encephalon, functionally associated with the neurocranium, and the skeletal muscles, functionally associated with the masticatory apparatus. The changes observed in DNA concentration suggest that protein deficit delayed muscle growth through a decrease in cell size rather than a decrease in cell number in the muscular fibre.