A prospective study of 40 patients for a period of 9 months was conducted, in order to evaluate the tolerance, clinical evolution and nutritional parameters in critical patients on enteral nutrition. In all cases, nutrients were administered enterally, by nasogastric tube and the administration method selected was continuous perfusion in most cases. 78.5 +/- 17% of estimated Kcal. were administered. During the study, the following aspects were studied: fasting time, type of diet, time during which enteral nutrition (EN) was maintained and reason for suspension, degree of derivation using nasogastric tube (NGT), number of bowel movements per day, antibiotic therapy ad gastric protection drugs as well as drugs administered for supporting mechanical ventilation and the evolution of the patient. Evolutional controls of the nutritional state were also conducted. Tolerance was seen to be good, especially in patients on continuous perfusion. With regard to the evolution of nutritional parameters, we observed maintenance of proteic levels with a slight recovery of retinol-binding protein (RBP) and no statistically significant differences between patients who died and those with a favourable development. The level of oligoelements was maintained, although below normal levels. CONCLUSIONS EN is the ideal selection for the nutritional support of critical patients with functionally usefull gastrointestinal tracts. A good digestive tolerance was observed, and proteic levels maintained were similar to the initial ones, although with this type of diet, we recommend an additional intake of iron.