The problems of microbial resistance and the increasing numbers of immunocompromised individuals have strengthened interest in new therapeutic strategies, including immunomodulation. Since phagocytes play both positive and deleterious roles in infectious diseases, they may be criticl targets in the study of drug-induced immunomodulation. Antimicrobial agents can modify phagocyte numbers] and functions in many ways. The main data and the implications of such interferences are reviewed in this paper.