Hi, I automated Alex's (thanks a lot, alex) script and finished my renumbering job :) > ruby renumber.rb xxxx.pdb step_size __START__ require 'bio' pdb = Bio::PDB.new(File.read(ARGV[0])) step_size = ARGV[1] pdb.each_atom do |atom| atom.resSeq += step_size.to_i end puts pdb __END__ K. Shameer