Code mobility has the potential to provide more flexible and efficient solutions to traditional distributed applications. However, developing distributed programs with code mobility is quite a challenge and so is the understanding of their dynamic behavior. Graphical visualizations are a promising way to help to understand the dynamic behavior of distributed applications, including those that contain mobile agents. This paper addresses two issues: what needs to be visualized and how do we visualize it. We present an innovative approach to visualizing code mobility in the context of processtime diagrams/message sequence charts. An infrastructure that provides tracing facilities and supports both on-line and postmortem visualization is discussed to demonstrate our approach.