The time course of lipid peroxidation (LP) products was studied in the heart, liver, and brain of rats exposed to 1, 6 and 12 h stress and compared with the extent of LP induction in these organs in vitro. It was shown that the LP activation in the internal organs with maximum in 1 h stress was accompanied by 2 fold decrease in LP products in the brain. More prolonged stress eliminated differences between tissues in all organs approaching the LP level to the control. The LP induction in vitro also revealed reciprocal relations between the LP intensity in brain and internal organs which remained in control group as well. Possible role of the LP suppression in brain induced by acute stress and significance of the phenomenon are under discussion.