The social amoebae Dictyostelium and human leukocytes possess the ability to polarize and move in a directed fashion in response to chemical signals. We are interested in understanding how cells transduce shallow external chemotactic signals into highly polarized cellular responses, which are required for directed cell migration. By tagging various signaling proteins with the green fluorescent protein (GFP) we have been able to visualize in live cells where and when various cascades are activated. This has led us to propose a novel mechanism that explains how chemotactic gradients are amplified by signal relay. Our research projects are designed to provide insight on the role of various signaling cascades in chemotaxis and have direct bearing on the understanding of clinically important processes as such leukocyte migration to sites of inflammation as well as cancer metastasis.