This study, which links into the most recent research on Karl Barth, deals with the significance of prayer for Karl Barth's theology. A key role is played in the analysis by the term "reciprocity." It shows that for Barth, prayer is to be understood as a dialogical event. The figure of reciprocity helps in clarifying the role of human activity and subjectivity in prayer. Thus it becomes clear that this dialogical event structure is a fundamental structure in Barth's theology.