Two mouse monoclonal antibodies (mABs), 25.31 raised against an subunit epitope of LFA1 antigen and Mol against an epitope of the complement receptor type 3 (CR3) were used for investigating their effects on human polymorphonuclear (PMN) functions. The two mABs have an inhibitory effect on PMN adherence. Furthermore, the PMN adherence strength depends upon the support and the adherence induces the capping process of these antigens. Other PMN functions dependent upon adherence were also altered by these two mAbs: random locomotion and that directed by formyl-methionyl-leucyl-phenylalanine (FMLP) or by activated serum, degranulation induced by opsonized or non opsonized zymosan but not by phorbol myristate acetate (PMA), iodination, K562 cell cytotoxicity. Luminol enhanced chemiluminescence of PMN was diminished by both mAbs when PMN were stimulated either by opsonized zymosan or by PMA. Our results confirm other workers' findings, and they are consistent with PMN functional abnormalities observed in children with congenital LFA1, Mol antigens defect.