Summary. Kwashiorkor, the human disease of proteinenergy malnutrition, has been implicated in the aetiology of malnutrition-related diabetes mellitus, a form of diabetes not uncommon in developing countries. We have previously demonstrated that temporary protein-energy malnutrition in young rats causes a persisting impairment of insulin secretion. The present study investigates whether this secretory deficiency is accompanied by structural alterations of the endocrine pancreas. Three-week-old rats were weaned onto semi-synthetic diets containing either 15 % or 5 % protein and these diets were maintained for 3 weeks. From 6 weeks of age all rats were fed a commercial chow containing 18 % protein. The endocrine pancreas was investigated by light and electron microscopic morphometry at 3, 6 and 12 weeks of age. In rats not subjected to protein-energy malnutrition there was a progressive increase, with age, of total pancreatic Beta-cell weight and individual Beta-cell size. In 6-week-old rats fed the low protein diet total pancreatic Beta-cell weight and individual Beta-cell size were diminished. In 12-weekold rats previously fed the low protein diet total Beta-cell weight remained lower compared to control rats. It is concluded that protein-energy malnutrition early in life may result in a diminished reserve for insulin production. This may predispose to glucose intolerance or even diabetes in situations with an increased insulin demand.Key words: Malnutrition-related diabetes mellitus, kwashiorkor, protein-calorie malnutrition, rat, pancreatic islets, pancreatic Beta cell, insulin, light microscopy, electron microscopy, morphometry.The relationship between affluent food supply, obesity and diabetes mellitus is well known and has been the subject of numerous studies. The observation made in 1907 [1] that the spectrum of diabetes in tropical regions of the Third World differs from that in western society and that the disease may be related to malnutrition is not as well recognized. However, in recent years the malnutritionrelated diabetic syndromes have been delineated and are now regarded as separate entities [2]. The exact role of malnutrition in the aetiology and pathogenesis of these types of diabetes remains obscure [3].Kwashiorkor, the disease of protein malnutrition in the young, is characterized by, among other symptoms and signs, impaired glucose tolerance and a diminished or even absent insulin secretory response to glucose [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. This appears to be a feature typical of protein deficiency, since balanced malnutrition, as in marasmus, has little or * This work was presented in part at the 26th Annual Meeting of the European Association for the Study of Diabetes in Copenhagen, Denmark 10-13 September 1990 no effect on glucose tolerance and insulin secretion [7,9,11,12,15,18]. Following nutritional rehabilitation, patients with kwashiorkor show a rapid improvement of glucose tolerance and insulin secretory response to glucose within weeks but short-term...