The invention relates to a method of detoxifying a lipopolysaccharide (LPS) or a lipid A from a Gram-negative bacterium, which comprises mixing the LPS or the lipid A with a cationic lipid so as to form a complex in which the LPS or the lipid A is associated with the cationic lipid. According to the conventional preparation modes, the cationic lipid with the co-lipid, if this latter is present, get(s) structured into complexes i.a. liposomes. When preparing lipidic complexes, the addition of LPS or Lipid A leads to an association of this latter with the cationic lipid and as a result, the LPS or lipid A is substantially detoxified. The LPS or lipid A detoxified by the complexes, e.g. when incorporated into liposomes, can be used as vaccinal antigen or as adjuvant.