Intestinal dysfunction commonly occurs following hemorrhage and injury and appears to contribute to the development of multiple organ system failure in this setting. In order to examine possible mechanisms leading to intestinal dysfunction following blood loss, we investigated mRNA levels for cytokines with proinflammatory and immunoregulatory properties (interleukin 1 β (IL-1β), IL-6, IL-10, TNF-α, TGF-β, IFN-γ) as well as mRNA expression for inducible nitric oxide synthase (NOS) over the 3 days following hemorrhage. Significantly increased levels of mRNA for IL-1β IL-10, and IFN-γ were found among cells isolated from Peyer's patches 3 days following hemorrhage. Amounts of mRNA for inducible NOS were not significantly altered 24 or 72 h after blood loss. In addition to being increased 72 h following hemorrhage, levels of mRNA for IL-10 also were increased 1 and 4 h posthemorrhage. No alterations in cytokine or NOS expression were found 24 h following blood loss. These results demonstrate that significant increases in proinflammatory and immunoregulatory cytokine mRNA levels among cellular populations in Peyer's patches are present at late posthemorrhage time points. These alterations in cytokine expression may contribute to the morphologic, immunologic, and functional changes in the intestines which are present following blood loss and injury.