One of the major achievements in modern medicine has been the development of research into antimicrobial agents. These drugs are now widely used in the treatment of human and animal infectious diseases caused by bacterial pathogens. However, some antibacterial agents, mainly macrolides, tetracyclines, and sulfonamides, have both anti-inflammatory and immunomodalotory properties. They can down-regulate prolonged inflammation, increase mucus clearance, prevent bacterial biofilm formation, and stimulate or impair the activation of the host immune system. It is possible that these drugs are able in modify phagocyte activity by altering their functions (chemotaxis, phagocytosis, oxidative burst, bacterial killing, and cytokine production). In addition, some antibiotics influence the biology of bacteria; they alter their metabolism, morphology, and antigenicity and inhibit the production of various virulence factors. The immunomodulatory and anti-inflammatory properties of antibiotics can occasionally be therapeutically useful in the treatment of chronic, noninfectious disorders, such as rheumatism, asthma, and other immunological diseases.