In this paper, we present an interactive system for visualization of three-dimensional scalar fields. The system has been designed in order to overcome some of the problems posed by very large volume data sets. The adopted solution exploits an efficient multiresolution data structure based on a tetrahedral domain decomposition. The mesh to be rendered can be selectively refined over areas that the user considers more critical, on the basis of either field values or domain locations. The system supports different rendering techniques, such as isosurface fitting and Direct Volume Rendering (DVR).