We have been using granule-poor anucleate fragments--cytokineplasts and U-cytoplasts--released from human peripheral blood polymorphonuclear leukocytes (granulocytes; PMN) to study cell functions that bear on aspects of the inflammatory response. The work is particularly aimed at the relationships among specific but overlapping areas of leukocyte activity: adherence, locomotion, target recognition, chemotaxis, penetration of endothelial monolayers, ingestion, the increased metabolic activity that ordinarily accompanies phagocytosis or other cell activation processes, degranulation of lysosomal structures, and intracellular killing. The ways in which these activities can be separated from one another may distinguish obligate interactions from mere concomitance, and may reveal the specific pathways by which cell function is altered. We have found that cytoplasts provide a unique way of looking at the composition and function of the cell's motile and killing machinery, in greatly simplified systems.