BASIS The need for nutritional support is at present beyond question, while the use of early enteral nutrition in critical patients admitted to Intensive Care Units is increasingly common and would appear to offer a set of advantages as nutritional support. PATIENTS Of a total of 26 consecutive enteral nutrition patients, 22 were studied prospectively (84.6%), and, through a nasal-gastric probe, were administered early high protein enteral polymeric diet with 25% of total calorific value from proteins, for an average of 10 days. The other four (15.4%) did not enter the study, according to the exclusion criteria established, and so were not taken into account in the statistics. METHOD A design was followed in which the diet was administered progressively until reaching 30 ml/kg/day, in a maximum of three days, during which aspects were analyzed dealing with tolerance and ease of use, on the one hand, and other metabolic and nutritional aspects on the other. Analytical controls were carried out on days 0, 4, 8 and 12. Tolerance and adverse effects were monitored continuously. RESULTS During the study, one of the twenty-two patients died (4.54%): the other 21 remained alive. In analysis of the metabolic and nutritional parameters, improvement was obtained in all those expected to reach normal levels, with p < 0.001 (glucose, prealbumin, TF, RBP, Zn, Mg and P). Of particular note was the evolution of the nitrogen balance (p < 0.001 and r = 0.77). As to tolerance, diarrhea appeared in two patients (9.09%), ileus in one (4.5%): no cases were detected of abdominal distension, nausea or vomiting. In no case was diet suspended for causes attributable to the enteral nutrition, nor was any therapeutic manipulation required. CONCLUSIONS Excellent tolerance of enteral nutrition was obtained, with almost no complications associated with its use, despite the gravity of the patients (APACHE 14). On the other hand, an improvement was obtained in metabolic and nutritional parameters, with the particular significance of the nitrogen balance.