In this paper, I will demonstrate how the Unified Modeling Language (UML) can be used to describe agent interaction protocols. The approach that is presented in this paper does not propose enhancements or completely new diagrams but instead relies on existing UML elements and the UML extension mechanism that is part of the standard. This conformity with the base UML is a major advantage of the idea as it prevents a diversification of the UML into different potentially incompatible dialects. The practical use of the method is demonstrated with an example on how to specify a realistic agent interaction protocol.