Direct recording of the kinetics of early phagocytic events, recognition or adhesion and ingestion, may better characterize some forms of polymorphonuclear leukocyte (PMN) dysfunction. This report describes a method and criteria to discriminate concurrently between adhesion and ingestion of Staphylococcus aureus by human PMNs at the level of the light microscope. The criteria were confirmed by several lines of direct evidence: low temperature and cytochalasin b treatment of PMNs; lysostaphin digestion of target Staphylococcus aureus after PMN incubation; and differential ingestibility of colony types I and III N. gonorrheae. Concurrent determinations of the initial kinetics of adhesion and ingestion of bacteria by PMNs demonstrated generalized first order kinetics, sensitive to bacterial challenge ratio and total particle density. Most importantly, the method may be applied to determine if phagocytically defective PMNs actually fail to recognize opsonized bacteria.