There are multiple causes of protein-energy malnutrition in maintenance dialysis patients. The requirements of protein in dialysis patients are higher than in healthy individuals, and the intake of protein and energy in relation to the requirements is frequently low. Anorexia may be caused by uremia and underdialysis. There is experimental evidence that dialyzable uremic toxins accumulate in renal failure and suppress the appetite. In addition there are several psychosocial and comorbidity factors that may hamper adequate nutrition. There are also several factors in dialysis patients that may enhance protein catabolism and increase protein requirements, such as low energy intake, metabolic acidosis, dialytic loss of glucose, protein and amino acids and other catabolic effects of the dialytic procedures, as well as effects of infections and other comorbidity factors. The relative importance of the various factors that cause anorexia and stimulate protein catabolism is still not well understood. (C) 1995 by the National Kidney Foundation, Inc.