Toll-like receptors are essential pattern-recognition receptors of the innate immune system. They recognize a range of conserved molecules of invading microorganisms. The innate immune system is developed to protect the host, but can be deleterious if activated uncontrolled or inappropriate, such as in sepsis with Gram-negative bacteria. New approaches for treatment, like inhibition of innate immune responses, may be beneficial for the outcome of such conditions. Toll-like receptor 4 associated with CD14 and MD-2, is the lipopolysaccharide (LPS)-receptor and one of the candidates for such intervention. We investigated the newly described cyanobacterial LPS analogue CyP as a potential inhibitor of Escherichia coli (E. coli) LPS-induced inflammatory response in porcine whole blood. Pro-inflammatory cytokines and soluble terminal complement complex, sC5b-9, were used as read-outs. CyP, in contrast to E. coli LPS, did not induce cytokine production using doses up to 1mug/mL whole blood, indicating a lack of agonistic effect of CyP. In contrast, CyP was an efficient LPS antagonist, dose-dependently and completely inhibiting E. coli LPS-induced TNF-alpha, IL-1beta and IL-8 production. CyP was a modest activator of porcine complement compared to LPS from other Gram-negative bacteria. When CyP was pre-incubated in porcine whole blood before adding whole E. coli bacteria, a modest, variable and non-significant inhibition of cytokines were seen, reaching an average inhibition of 44% for IL-1beta. We have demonstrated for the first time that the cyanobacterial LPS analogue, CyP, is an efficient inhibitor of E. coli LPS-induced cytokines in whole blood and may be a candidate for therapeutic LPS-inhibition.