Gaining wide acceptance for the use of agents in industry requires both relating it to the nearest antecedent technology (objectoriented software development) and using artifacts to support the development environment throughout the full system lifecycle. We address both of these requirements using AUML, the Agent UML (Unified Modeling Language) — a set of UML idioms and extensions. This paper illustrates the next steps of our approach by presenting notions for the internal behavior of an agent and its relation to the external behavior of an agent using and extending UML class diagrams. General Terms Algorithms, Documentation, Design, Reliability, Standardization, Languages, Theory. Keywords Agents, UML, internal behavior of agents, AUML, design artifacts, software engineering.