Damaged intestinal mucosa in patients with extensive burns is one of the causes of the development of SIRS and MOFS. No unequivocal method has been established so far for assessment of the extent of damage of the intestinal mucosa. In the presented work the authors focus their attention on assessment of intestinal permeability in rats with burns. As their experimental method they used the lactulose-mannitol test (LAMA test). The animals were subjected to a deep burn with an extent of 20% body surface (TBSA). Then the LAMA test was performed 24, 48 and 72 hours after the burn. The rats were divided into groups: the first with a burn without enteral nutrition, the second with a burn and polymeric enteral nutrition and the last with oligomeric enteral nutrition. From the conclusions it is evident that a burn extending over 20% TBSA causes in the laboratory rat to experience impaired intestinal permeability. The work did not prove a significant difference between groups with and without enteral nutrition. Due to its simplicity speed, repeatability and high yield the LAMA test is a method which can be used in patients with burns in departments for the treatment of burns.