Ten years ago interest in leukocyte chemotaxis was restricted to a relatively small group of scientists whose interests were quite circumscribed. In the past decade both the number of workers and their publications has grown at some- thing approaching an exponential rate and, more importantly, the field has gradually expanded to encompass a large number of diverse areas (mediators, receptors, cell effector mechanisms, regulatory factors, etc.). It is now apparent that leukocytes are particularly useful for studies of the locomotory behavior of all cell types and of mechanisms controlling cell...