A technique to extract solid isosurfaces from three-dimensional electron density data at high speed is presented. The ability to change the contouring threshold in real time renders the method a powerful tool for interactive analysis of proteins and their supramolecular assemblies, in order to compare and combine structural information gathered by different data acquisition methods. Chemical properties can effectively be mapped onto these isosurfaces by the use of texture mapping. The implications of these methods in combination with other visualization techniques are discussed, and a framework for their integration into a general-purpose molecular graphics toolkit is proposed. (C) 1996 Academic Press, Inc.