Abstract Using the reverse transcriptase-polymerase chain reaction (RT-PCR), we investigated the influence of restraint stress on the expression of the mRNA for interleukin-6 (IL-6) and the mRNA for the IL-6 receptor (IL-6R) in the rat brain. After rats had been restrained for 4 hours, the hypothalamus and midbrain were removed at fixed intervals up to 24 hours, and levels of IL-6 mRNA and of IL-6R mRNA in these regions were determined by RT-PCR. Restraint stress significantly enhanced the expression of IL-6 mRNA and reduced that of IL-6R mRNA in the midbrain, whereas the stress caused the reduced expression of IL-6R mRNA without any change in the level of IL-6 mRNA in the hypothalamus. After the stress, the expression of mRNAs for IL-6 and IL-6R continued to diminish in both regions. These findings indicate that the levels of mRNAs for both of IL-6 and IL-6R in the rat brain can be influenced by restraint Stress.