Thanks Elaine, Tom. This is of course for "quick and dirty" helical structures where I want to take a single chain and replicate it dozens of times while imposing symmetry to create a short segment of a fiber. The MODEL and ENDMDL are good suggestions, as well as the /dev/null redirect. I suppose there are scenarios when one would want to know about duplicate atoms, but in my case there are just so many that it is pointless to print them all out. The ultimate solution here is really for me to not to be so lazy ;) As an aside, I typically use the program pdbsymm which is included with the SITUS package to impose the symmetry to generate an arbitrary number of symmetry mates along a helical axis (using polar coordinates). It simply replicates the original PDB file while updating the coordinates, thus I have the duplicate numbering problem. But your suggestions should do the trick in the meantime. Thanks again. Albion