Hi Esther, Chimera does not know how to read the MolMol potential file header. But the MolMol format is very simple and you could edit it to a similar format the APBS electrostatic potential format and use that file in Chimera to color a molecular surface. Here's the MolMol potential format as described in the ReadPot manual page: http://www.scl.kyoto-u.ac.jp/scl/appli/appli_manual/molmol/help/html/ReadPot... x0 xSize xInc y0 ySize yInc z0 zSize zInc val val val .... and here is an example APBS file: # Data from APBS 0.3.2 # # POTENTIAL (kT/e) # object 1 class gridpositions counts 65 97 97 origin -8.064450e+00 -4.768105e+01 -4.266980e+01 delta 3.779047e-01 0.000000e+00 0.000000e+00 delta 0.000000e+00 4.098240e-01 0.000000e+00 delta 0.000000e+00 0.000000e+00 4.099125e-01 object 2 class gridconnections counts 65 97 97 object 3 class array type double rank 0 items 611585 data follows 8.921700e-01 9.000006e-01 9.078676e-01 .... I believe if you replaced the first lines of the MolMol file with: object 1 class gridpositions counts xSize ySize zSize origin x0 y0 z0 delta xInc 0 0 delta 0 yInc 0 delta 0 0 zInc data follows val val val ..... and make the file suffix ".dx", then this would be read in Chimera as an APBS potential file and could be used for coloring. The MolMol format could be added into Chimera so this file editing is not needed but I wonder if enough people would use that to make it worth writing code for. I'll add it to our list of requested features. Tom