<p>The aim of this study was to determine whether long-term housing in an enriched environment can reduce the adverse consequences of early proinflammatory stress on the social behavior of adult male rats. On postnatal days (PND) 3 and 5, Wistar rats were given either lipopolysaccharide at a dose of 50 μg/kg (the LPS group) or physiological solution (the PS group). Starting from PND 30 and continuing to the end of the experiments, some of the rats lived in environmental enrichment (EE) and the other part in standard conditions (STAND). Testing for social dominance in pairs of rats in a tube revealed that when kept in EE, the PS and LPS groups had fewer wins than similar groups of rats kept in STAND conditions. Males of the LPS group stopped winning under the influence of EE in PS–LPS pairs. In the resident-intruder test, the males of the LPS group kept in EE had smaller numbers of attacks, rearings, sexual assaults, and durations of intruder pursuit, while rats of the PS group, conversely, had a higher number of attacks than when kept in STAND conditions. Analysis of cytokine gene expression showed that in rats of the PS group, but not in those of the LPS group, being kept in EE led to higher levels of expression of mRNA for the anti-inflammatory cytokine TGF-β1 in the dorsal hippocampus and amygdala, while higher levels of expression were obtained for the proinflammatory cytokine IL-1β in the prefrontal cortex, as compared with STAND conditions. Thus, being kept in EE had a beneficial effect on the behavior of rats of the LPS group, reducing dominance properties and aggressive behavior.</p>