Antibiotics represent a key component of treatment for severe bacterial infection. Bacterial lipopolysaccharide from Gram-negative organisms is now well recognized to be a potent microbial toxin that plays a critical role in the initiation of the proinflammatory events that contribute to the pathogenesis of the disease. Pseudomonas aeruginosa, Haemophilus influenza and Escherichia coli were exposed to 0.5 MIC and 5 MIC of Imipenem, Aztreonam, Gentamicin and Polymyxin B for 2 and 5 h. Variable amounts of endotoxin were released after exposing the organism to antibiotic. Aztreonam at a concentration of 0.5 MIC with exposure period 5 h, induced the release of substantial amounts of endotoxin from all organisms and decreased amounts of endotoxin by Gentamicin while Imipenem and Polymyxin B induced the release of negligible values under the same conditions.