The possibility that antibacterial agents, primarily directed against microorganisms, also modify host functions is widely recognized. While a knowledge of these non-antimicrobial effects of antibiotics, sometimes considered as 'side-effects', is necessary to prevent antibiotic-associated toxicity, the development of drugs derived from antibacterial agents for use in non-infectious diseases (e.g. motilins and antidiabetic drugs) is a new field of therapeutic research. Interactions between antibacterial drugs and the immune system may contribute to therapeutic efficacy in infectious diseases [1,2]. The immune system itself is a complex pyramid of redundant cellular factors/humoral effectors/mediators, whose fine regulation is just beginning to be unraveled. Phagocytes, ubiquitous and multifaceted cells are key components of cellular immunity, being involved both in immediate defences against non-self targets (pathogens, tumour cells, exogenous molecules, etc.) and in the regulation and triggering of specific immune responses. They are thus, prime targets of immune response modifiers. This review reconsiders the widely explored problem of interactions between antibacterial agents and phagocytes, focusing on future prospects in both infectious and non-infectious diseases.