ebXML is becoming the new international standard for the specification and deployment of complex B2B transactions over the internet. ebXML transactions are inherently distributed, involving many actors exchanging XML messages with each other according to complex flows and rules. This complexity hampers validation of the correctness of a modelled business transaction by business experts. To alleviate this problem, we have developed a tool set, consisting of a CASE tool for modelling ebXML transactions and an animator for validating the modelled transactions. At the specification level, the main UML models used are class diagrams to model messages and an activity diagram to model the global flow of the messages that are exchanged by the actors (companies). The animator is internet-based, thus supporting distributed animation of an ebXML transaction. The animator checks business rules on the messages exchanged during animation. Moreover, the animator annotates messages with possible responses. Heart of the animator is a workflow engine that can read workflow descriptions in XPDL. The animator is configured automatically from the UML specification models. We illustrate the whole approach on a real-life example.