Hi Wayne > >>>> molSystem = ... # similar to the above >>>> chain = molSystem.findFirstChain(code='A') # if the A chain >>>> residues = chain.sortedResidues()[23:] # if you want to renumber 23+ > # but remember that 23 has seqId 23+1=24 so be careful >>>> for residue in residues: >... residue.seqCode = residue.seqCode + 2 >... >>>> This python code works great. Thanks for all your help Cheers Ben