An approach to infections in cancer patients is outlined that divides such infections into those due to underlying disease, those related to underlying disease plus therapy, and those related to therapy alone. The incidence of such infections in each of the categories is discussed, together with a general outline of patterns and trends in regard to involved microorganisms. Several specific areas discussed include: problems of superinfection with newer antimicrobial agents; the current inadequacy of diagnostic techniques; the potential for early treatment with monoclonal antibodies; the potential for augmenting one or more host defenses prior to sundering other defenses during antitumor chemotherapy; the potential value of a variety of nutrients that either may be depleted or might be of benefit in enhancing host defense mechanisms.