With reference to recent bibliographical data and their own experience, the authors discuss the existence of three major mechanisms (models) in toxi-infectious aggression, namely: -- direct, cellular, performed by toxin-enzymes, aggressins, hemolysins, invasins, cytopathogenic effects; -- unspecifically mediated (by nervous or humoral mediators); -- specific mediators (by immune effectors, humoral immunoaggressive mechanisms or cellular induced mechanisms). The text is illustrated by examples with reference to aetiological entities than can be listed in the corresponding pathogenetic system and therapeutical lines.