The complement system plays an important role in protection of higher organisms against bacterial infection. Lysozyme cooperates with the complement system in the bactericidal action of serum. Adsorption of serum onto bentonite (montmorillonite, MMT) is well known procedure to remove the lysozyme from serum. Our present results show that the most efficient killing of Salmonella O48 occurred when all components of normal human serum (NHS) cooperated with each other. It is very interesting that elimination of lysozyme from NHS by using MMT significantly decreased the bactericidal activity of NHS against Salmonella O48 strain. The results of X-ray diffractometric studies suggested that apart from lysozyme, other components of serum were adsorbed on the bentonite particles.