The development of experimental acute pancreatitis (EOP) in rats is accompanied by (i) intensification of the lipid peroxidation (LPO) process and the accumulation of malonic dialdehyde (MDA, an LPO product) in the tissues of pancreas, liver, and kidney and in the blood serum, (ii) destabilization of membranes and reduction of the osmotic resistance of erythrocytes (ORE), (iii) increase in the concentration of extracorpuscular hemoglobin (ECH) and medium-molecular-weight molecules (MWM) in the blood serum, and intensification of protein autolysis in tissues. Preliminary triple intraperitoneal administration of a delta-sleep-inducing peptide (DSIP) in a dose of 12 micrograms/100 g body weight to the test rats with EOP stabilized LPO, improved the erythrocyte membrane structure, reduced the MDA level in tissues and blood serum, increased ORE, reduced the ECH and MWM level in the blood, and decreased the protein autolysis rate in tissues.