Some of the many antimicrobial agents (beta-lactams, macrolides, aminoglycosides, tetracyclines, new quinolones; NQs) were reported to have a bactericidal or bacteriostatic effect cooperating with host defense mechanisms including polymorphonuclear neutrophils (PMNs). We investigated the effect of new quinolone antimicrobials on chemiluminescence (CL) response of human PMNs. Among many NQs, we chose ofloxacin, lomefloxacin, fleroxacin, sparfloxacin, AM-1155, NM-394, Q-35, Y-26611 and T-3761. Twenty-five or 100 micrograms/ml of fleroxacin and ofloxacin enhanced luminol-dependent CL response of PMNs up to 1.5-2.0 times compared to the drug free condition. Other antimicrobial agents, however, inhibited CL response. This suggested that fleroxacin and ofloxacin were more efficient in the treatment of bacterial infections with respect to the interaction between antimicrobials and PMNs.