Antimicrobial agents can act as immunomodulators, whether it is by direct interaction with immune cells, or indirectly through the release of bioactive fractions by sensitive microorganisms belonging to the microbiota (particularly intestinal). The studies carried out have allowed immunopotentiator, immunosuppressor and anti-inflammatory effects to be established in different antibiotic groups. Knowledge of this capability to modulate the biological response is very important at the time of choosing the most suitable antimicrobial agents to treat a particular infection, whether in immunocompetent or immunocompromised subjects. In this line of research, experimental in vitro and in vivo models are applied to the study of the biological response modification by antimicrobial agents.