Knowledge workers are often embedded in an organizational setting, where execution of processes allows for appropriate, context-sensitive support. When a knowledge worker starts a new task in a workflow management system, chances are good, that someone of his colleagues has already performed or is currently busy with a similar task. Our research aims at enabling a knowledge worker to make use of workflow tasks in a minimally disturbing way. Therefore, we have to elicit his task context and find out workflow tasks with similar context. As such a task context consists of a set of contextual elements, a technique to compare two task contexts and the contextual elements therein is needed. This paper presents a similarity measure for these contextual elements, and hence, for task contexts.