Two groups of 10 patients with an identical mean injury score (25 + 5) were treated from day 3 after injury until day 10 with a whole protein high caloric (WPHC) diet (group A) or with a peptide diet (PD) (group B). Intake of calories, protein, water, Na+ and K+ was measured daily as well as excretion of urine, Na+ and K+. Gastric reflux, bowel movement and plasma levels of Na+ and K+ were registered and the nitrogen balance and Na+/K+ quotient in urine were calculated daily. Clinically both diets were well tolerated, with low gastric reflux and no diarrhea. The calculated caloric demand could be covered in group A on day 7 post-injury (or day 4 of enteral nutrition) and in group B on day 11 post-injury (or day 7 of enteral nutrition). The caloric intake in group A remained significantly higher on days 4-10. There was no difference in nitrogen balance. Total enteral Na+ and fluid intake were significantly lower in group A, but some additional parenteral Na+ had to be given to keep plasma Na+ levels in the normal range. There was no difference in urine output between the 2 groups; therefore, there was a significant fluid retention in group B. Interestingly, the Na+/K+ quotient in urine was significantly higher in group A. The low Na+ intake might influence the back flow of interstitial edema in the 'flow phase'. This diet seems to be adequate, especially for the nutrition of burn patients and of patients with cardiac disease, and can cover the high caloric needs of polytraumatised patients within a few days.