This is an in vivo study of chemotaxis (directed locomotion), aimed at understanding the process by which blood neutrophils (PMN) find their way to areas of inflammation/infection. It employs the unique chemotactic system of Professor Marcel Bessis, in which a red blood cell destroyed by laser microirradiation gives rise to a chemotactic gradient, up which PMN migrate. The system allows for a zero time (the laser flash), and direct observation of the orientation, adhesive properties, trajectories, and interactions of every cell in the field. To this is added superb optics, light enhancement when desired, video recording in real time or time lapse, in gray scale or pseudocolor, and computer-assisted analysis of the behavior of individual or groups of cells. Also employed in this system are a nucleate, motile, granule-poor fragments (cytoplasts) derived from PMN, which represent simplified systems in which to study chemotaxis. The present work is addressing, in PMN and in PMN cytoplasts, such problems as the effects on chemotaxis of agents that inhibit the generation of the radical gas nitric oxide (N)), the effects of defined substrates such as glass coated with the important extracellular matrix proteins, fibronectin and vitronectin, and the role of [Ca2+]i transients in the ability of PMN and of cytoplasts to detach from substrate and therefore proceed up the gradient. In the aggregate, these studies should teach us a great deal about the requirements for chemotaxis; possible ways in which extracellular matrix proteins may help in the recruitment of inflammatory cells; and how nitric oxide, a radical gas of intense current interest, may figure in these events.