Although studies have shown that the gut is capable of being a cytokine-producing organ and that the proinflammatory cytokines TNF-α, IL-1β, and IL-6 are upregulated following the onset of sepsis, it remains unknown whether the gut is indeed the major source of the increased cytokine production under such conditions. To determine this, male rats were subjected to cecal ligation and puncture (CLP, a model of polymicrobial sepsis) or sham operation followed by the administration of normal saline solution subcutaneously (i.e., fluid resuscitation). Systemic and portal blood samples were taken simultaneously at 2, 5, 10, or 20 h after CLP or sham operation. Plasma levels of TNF-α, IL-1β, and IL-6 were determined using an enzyme-linked immunosorbent assay. In additional animals, the small intestine was harvested at 10 h after CLP or sham operation and examined for TNF-α, IL-1β, and IL-6 gene expression by RT-PCR. The results indicate that the levels of TNF-α, IL-1β, and IL-6 in both systemic and portal blood samples were significantly elevated during sepsis with the exception that the increase in IL-1β was not significant at 2 h after CLP. However, there were no significant differences in the levels of those proinflammatory cytokines between systemic and portal blood at any points after the onset of sepsis. Moreover, there were no significant alterations in the proinflammatory cytokine gene expression in the small intestine at 10 h after CLP. Since the levels of TNF-α, IL-1β, and IL-6 were not significantly increased in portal blood as compared to systemic blood and since there was no upregulation of gene expression for these cytokines, it appears that organs other than the gut are responsible for the upregulated proinflammatory cytokines during polymicrobial sepsis. Copyright (C) 1999 Elsevier Science B.V.