Neutrophil granulocytes are most active producers of potentially toxic free oxygen radicals. Since other functions of granulocytes can be affected by lymphokines or monokines, we investigated whether granulocyte oxygenation activity can also be influenced by such cellular mediators. Human granulocytes emitted strong chemiluminescence after addition of culture supernatants from human mononuclear cells stimulated with bacterial lipopolysaccharide (LPS). Response of the granulocytes was dose-dependent and was inhibited up to 90% or more by superoxide dismutase. This granulocyte chemiluminescence inducer-activity (GCI-activity) in the LPS-induced supernatants was heat-labile and sensitive to trypsin treatment. Addition of cycloheximide to the cultures inhibited the generation of GCI-activity by 80%. On HPLC gel filtration GCI-activity eluted with two distinct peaks corresponding to molecular weights of 60 +/- 10 KDa and between 1 and 5 KDa. Murine interleukin 1, human recombinant interferon-alpha and -gamma were devoid of GCI-activity. When mononuclear cells were fractionated by plastic adherence or counterflow elutriation, monocytes appeared to be the source of GCI-activity. Therefore, it appears that granulocyte oxygenation activity can be enhanced strongly by a cellular mediator derived from monocytes. This interaction of monocytes and granulocytes may constitute a new and potent pathway of phagocyte-dependent production of highly reactive and potentially toxic oxygen radicals.