In the Tenth Doctor's words, this was achieved by:
- "[using] hypersonic sound waves to destabilise the cell structure, then a metagenic programme to manipulate the coding in the protein strands. Basically, he hacked into his own genes and instructed them to rejuvenate."
Harold Saxon, the human alias of the Master, supported Lazarus's research so that he could copy, improve and focus the technology into his laser screwdriver and reverse it to, instead of rejuvenate people, make them older. (TV: The Sound of Drums)