Locating code within large systems, especially when the code is unfamiliar to a developer, may consist of an expensive activity. The GUITA Toolkit¹ consists of a set of Java instrumentation components, which can be woven into an application, in order to supply the developer with program comprehension mechanisms that can be activated at runtime by interacting with the application. This demonstration covers two of these mechanisms, which can be used in combination: (a) GUI-driven code tracing, which enables UI widgets to be traced to their representation in the source code at runtime, and (b) feature-driven code tracing, which enables code fragments to be located by demonstrating a feature on the executing application.