This study was conducted to evaluate renal insufficiency as an independent risk factor for malnutrition. Furthermore, the metabolic effect of an increase in the calorie-nitrogen ratio of realimentation formula was studied in malnourished elderly patients. During a 12-month follow-up period, nutritional status and renal function were determined in 296 patients consecutively admitted to the geriatric ward. The subgroup of 81 patients with a creatinine clearance below 30 ml/min, was older, had a lower body weight and decreased values for pre-albumin. However, renal insufficiency could not be identified as an independent risk factor for malnutrition. 67 malnourished but metabolically stable patiënts in need for nutritional support were prospectively randomized (stratified for age and renal function) to receive an isocaloric enteral feeding with 80 gr, 52 gr or 35 gr protein content for 2000 kcal. A regimen of 52 gr protein caused an improvement of the nutritional status and a positive nitrogen balance. With the formula of 35 gr protein, on the contrary, there was a negative nitrogen balance whereas the 82 gr formula caused a positive balance but an increased nitrogen excretion. A daily administration of 50 gr protein for 2000 kcal is sufficient for nutritional support and represents no supplementary burden on renal function, which is already reduced physiologically by age.