This is what I did: require 'bio' serv = Bio::Fetch.new() entry = serv.fetch('pdb', '1w6k') pdb = Bio::PDB.new(entry) The last step use up all memory and quit. The pdb file is quite big and I only need the information from header. Is it possible to do something like this ? pdb = Bio::PDB.new(entry[0-40000]) Thanx for the help