Nine different candidates of nuclei are being considered in experiments to confirm neutrinoless double beta-decay: 48 C a , 76 G e , 82 S e , 96 Z r , 100 M o , 116 C d , 130 T e , 136 X e , 150 N d . They all have arguments for and against their use in an experiment. Factors to be included and revised are natural abundance, reasonably priced enrichment, and a well understood and controlled experimental technique. The higher the Q -value, the better are the chances of a discovery, in principle. The phase-space factor G 0 ν ν , and thus the decay rate, grows with Q 5 .