Unfractionated heparin (UFH) and low molecular weight heparin (LMWH) are highly sulphated proteoglycans widely applied as anticoagulant drugs. They represent pivotal agents for the prevention and treatment of thromboembolic disorders, pulmonary embolism, disseminated intravascular coagulation and unstable angina. Several different studies have suggested that aside from their anticoagulant capacity, heparins possess anti-inflammatory properties, however reports have been conflicting. UFH and sulfated heparin derivatives have been shown to inhibit pro-inflammatory cytokine gene expression in lipopolysaccharide (LPS)-stimulated human mononuclear cells and to inhibit the nuclear factor-kB (NF-κB) activation in a tumor necrosis factor alpha (TNF-α) stimulated human endothelial cell line. However, other studies indicate that heparin in fact amplifies the inflammatory cytokine release in monocytes. Nevertheless, heparin appeared in several clinical trials to have the potential to treat inflammatory bowel disease, arthritis, rhinitis, and human asthma, with an anti-inflammatory effect dissociable from its anticoagulant activity. In the present study, we assessed the effect of LPS stimulation on heparin pre-treated and untreated pure human monocytes. Cells were isolated from whole blood and resuspended in RPMI supplemented with 10% platelet free autologous serum, before addition of unfractionated and low molecular weight heparins (1IU=10μg/ml and 0.1IU=1μg/ml per million cells) 15 minutes before LPS stimulation (1ng per million cells). Pro-inflammatory cytokine levels produced were measured by ELISA and NF-κB translocation using the TransAM Chemi Transcription Factor Assay. The production of TNF-α, interleukin (IL)-8, IL-6 and IL-1β was upregulated by LPS, and their levels significantly reduced when the cells were exposed to heparin, up to 3 fold with 0.1IU UFH. LPS-induced NF-κB translocation from the cytoplasm to the nucleus was also significantly reduced in heparin pre-treated cells; even at low heparin doses, as shown by a 1.5-fold reduction induced with 0.1IU UFH. NF-κB activation, a critical phenomenon in host inflammatory response, is implicated in a wide range of inflammatory diseases and therefore represents an ideal and novel molecular target. Here we report that both unfractionated and low molecular weight heparins possess the equal ability to significantly reduce the monocytic inflammatory reaction through inhibition of NF-κB activation. This indicates a potential mechanism responsible, in part, for the protective effect of the drug in inflammatory disorders. In clinical practice, heparin use as an anti-inflammatory agent is restricted by its potential to induce bleeding complications. Further investigations are required to elucidate the precise mechanism of action of the drug at the cellular level, and optimise the development of non-anticoagulant variants.