A successful immune response depends on the capacity of immune cells to travel from one location in the body to another--these cells are rapid migrators, travelling at speeds of microm/minute. Their ability to penetrate into tissues and to make contacts with other cells depends chiefly on the beta2 integrin known as LFA-1. For this reason, we describe the control of its activity in some detail. For the non-immunologist, the fine details of an immune response often seem difficult to fathom. However, the behaviour of immune cells, known as leukocytes (Box 1), is subject to the same biological rules as many other cell types, and this holds true particularly for the functioning of the integrins on these cells. In this Commentary, we highlight, from a cell-biology point of view, the integrin-mediated immune-cell migration and cell-cell interactions that occur during the course of an immune response.