The long-term effects on growth, glucose tolerance and insulin secretory response to glucose of temporary malnutrition early in life have been investigated. Rats were weaned onto either normal diet (18% protein), a protein-restricted diet (5% protein) or a diet adequate in protein but restricted in amount to equal the energy intake of protein-restricted rats ("energy restriction"). From 6 weeks of age and onwards all rats were fed normal diet. Body weight gain was inhibited by both protein and energy restriction but growth was resumed when rats were transferred to normal diet. Protein restriction impaired glucose tolerance and blunted insulin secretory response to glucose. Following refeeding glucose tolerance was normalized but insulin secretory response remained impaired at 12 weeks of age. Energy restriction did not initially affect glucose tolerance and insulin secretion. However, after refeeding male energy restricted rats developed a delayed and exaggerated insulin secretory response to glucose without concomitant deterioration of glucose tolerance. It is suggested that temporary protein restriction at a young age impairs pancreatic B-cell function and decreases peripheral sensitivity to insulin. By contrast, temporary energy restriction does not directly affect B-cell function but confers insulin resistance and compensatory increases of the insulin secretory response to glucose later in life. These models of malnutrition offer possibilities to further study long-term effects of early nutritional insults.