You have been very helpful in explaining different items that use the command line. I have a PDB file that was determined by NMR. Thus there are a large number of chains number as pdb (#0.1) Chain A etc. So I know that I can select a single chain, and build up an image with Chains A, B, etc using the #0.1 chain number. I want to visualize three Gly residues in one chain. So I learned that I can use the command ribbackbone to visualize the backbone atoms of the amino acids that I want to show. So when I use that command all the backbone atoms of the residues selected are visualized including the side chains. I also know that if I use the command ~ribbackbone all the backbone atoms are suppressed leaving only the atoms of the side chains. I know that without any residues or atoms specified the command applies to the whole model. Now as I said that I want to visualize three Gly residues in one of the chains. The Gly residue numbers are 33, 37, 38. They are on Chain #0.1 K. The information on the ribbackbone in the Chimera users guide, indicates that I should be able to do this by using parameters termed atom-spec. i.e. ribbackbone atom-spec <frameatom_spec.html> I looked elsewhere for how to designate the parameters for atom-spec and tried a few things, but I was not able to achieve the specificity of showing the backbone atoms of only the Gly residues. I don't think that I have to indicate that I want only the Gly residues in Chain K #0.1 because I can select the Gly residues from the sequence of Chain K #0.1. So after this long description of what I want to do, would you kindly inform me of how I can visualize the backbone atoms of only Gly. Thank you Arthur G. Szabo