Imipenem, a new antibiotic beta-lactam, and Tienam (an Imipenem/Cilastatine combination) have been studied in vitro and in vivo respectively, in the phagocytic function of macrophages. In this paper we have seen the variations produced by 50 mg/l of Imipenem and 120 mg/kg of Tienam in the adherence, spontaneous mobility, chemotaxis, opsonization, phagocytosis of Candida albicans and latex beads, candidicid effect and nitroblue tetrazolium (NBT) reduction in peritoneal macrophages from BALB/C mice. This antibiotic significantly increases in vitro and in vivo the adherence, spontaneous mobility and chemotaxis, phagocytosis of latex beads and the digestion of ingested material (nitroblue tetrazolium reduction) in the above-mentioned cells. The number of Candida albicans opsonized and ingested by the macrophages is not modified in the presence of Imipenem, and neither is the candidicid effect.