Lipopolysaccharide or endotoxin (LPS) is an amphiphilic macromolecule which constitutes the outer membrane of gram negative bacteria.During infection, LPS is released from the bacteria, over-stimulating the immune system (IS) response leading to septic shock.Released LPS molecules form lyotropic aggregates which exert the toxic activity.Aggregates¿ toxicity can be neutralized by antimicrobial peptides(AMP) which are thought to interact and modify LPS structures.Previous experiments revealed that SANS/TEM combination is suitable for these studies.Our proposal intend to study the aggregates of defined LPS molecules(from different bacteria). LPS aggregates will then be challenged by three AMPs of biological relevance.The aim is to assess AMPs¿ effect on LPS aggregate¿s structure.TEM and in-vitro toxicity test will corroborate SANS results to understand better AMPs¿ anti-endotoxic effect.