Standard client-server workflow management systems have an intrinsic scalability limitation: the central server is a bottleneck for large scale applications. It is also a single fault point that may disable the whole system. We propose a fully distributed architecture for workflow management systems. It is based on the idea that the case (an instance of the process) migrates from host to host, according to the process definition specification, as the corresponding activities are executed. This basic architecture is improved so that other requirements for Workflow Management Systems, besides scalability, are also contemplated. A CORBA-based implementation of such architecture is discussed, with both its limitations and positive points described.