Hi Lu, I think I know why the volume planes are slightly transparent for you. You are using Chimera version 1.2422 and I changed the volume solid rendering transparency behavior in the later Chimera version 1.2434 (August 3, 2007). You can either get the most recent Chimera from the daily builds web page: http://www.cgl.ucsf.edu/chimera/alpha-downloads.html Or in older Chimera versions use volume menu entry Features / Brightness and Transparency and change transparency to 0. You'll have to type this in the entry field and press return because the slider does not go all the way down to zero. This transparency value modulates the transparencies given by the height of the brightness / transparency yellow curve on the histogram. Newer Chimera changed the modulation behavior to keep completely opaque voxels still completely opaque while older Chimera did not. Tom