There is growing evidence that certain antibiotics exert their beneficial effects not only by killing or inhibiting the growth of bacterial pathogens but also indirectly by immunomodulation. This review aims at giving an overview of the immunomodulatory properties of antibiotics in different diseases: The antiinflammatory properties of macrolides in chronic inflammatory pulmonary disorders were recognized more than 15 years ago and have been well documented in the last decade. Recent data suggest that several antibiotics such as tetracyclines and cephalosporins may have a beneficial immunomodulatory or neuroprotective effect on neuroimmunological and neurodegenerative diseases including multiple sclerosis and amyotrophic lateral sclerosis. Moreover, the non-bacteriolytic but bactericidal antibiotics rifampicin, clindamycin and aminoglycosides kill bacteria without releasing high quantities of proinflammtory cell wall components. The use of bactericidal, non-bacteriolytic protein synthesis inhibitors reduces mortality and long-term sequelae in experimental bacterial sepsis, plague and meningitis. Clinically, macrolides have been well established as an adjunctive treatment to beta-lactam antibiotics in pulmonary diseases. For other indications, appropriate clinical trials are necessary before using the immunomodulatory properties of antibiotics in clinical practice.