Hi Miguel, The only Chimera tool for coloring a molecular surface using data values from a 3 dimensional grid is the DelphiViewer extension. It can read Delphi and GRASP grid files. As you say the GRASP format requires the grid size to be 65x65x65. The Delphi format which is almost the same allows any grid size but apparently GRID cannot produce that format. To determine if a GRASP grid is covering your molecule, open it in Chimera with File/Open using file type "Delphi or GRASP potential". This will display an isosurface and a white bounding box showing the extent of the grid. You can open your molecule and visually see how well it covers. Chimera can read several other volumetric data formats (CCP4, MRC, CNS, XPLOR, SPIDER, DOCK, PRIISM, ...) but these cannot be used to color an MSMS surface. You can display isosurfaces, or translucent solid representations with the Volume Viewer tool. I don't know if any of the GRID output formats for Chem-X, Frodo, Insight, Molcad Quanta or Sybyl are equivalent to any of the formats Chimera knows. We are interested in making it possible to color an MSMS surface using any of the volumetric data formats Chimera can read. I could add something to Chimera that does this. But it looks like it would also be necessary to add some file reader for some format that GRID produces. I saw that GRID has a K2A program that outputs the grid data in ascii. A relatively simple program might convert that to Delphi format for use with the current Chimera DelphiViewer extension. Tom