Abstract: Virtual Reality (VR) provides a useful tool for understanding complex, unsteady flow phenomena. The user can directly interact with the data and therefore benefits from a spatial coherence of action and result. However, visualization in virtual environments imposes very high demands on interactivity in order to maintain this coherence. Exploration of large, unsteady datasets in VR requires efficient visualization or data reduction algorithms to produce results within acceptable waiting times. We propose a technique for reducing required data especially suited for direct interaction in virtual environments. We use a distributed system to parallely extract a dynamic region of interest (DROI) from the simulation data. This DROI is adapted according to the user's interaction behavior and allows for the analysis of local flow features. With this reduction we provide interactive extraction of local features from large, time-varying datasets.