The UML suggests the employment of use cases for capturing the requirements and for specifying the interaction between the users and the system being modeled. Use cases are easily understood by users since they are essentially textual descriptions, but lack the precision and the conciseness accomplished by the other diagrammatic tools of UML. Besides, there is no systematic method that helps the designer to obtain such UML diagrams from a set of use cases. In this paper we present a diagrammatic tool to represent the users/system interaction called User Interaction Diagram (UID). UIDs have proven to be a valuable tool to gather requirements since they describe the exchange of information between the system and the user in a high level of abstraction, without considering specific user interface aspects and design details as in other UML diagrams. We show how UIDs can be incorporated into the requirements and analysis workflows of the Unified Process for software development.