Bloom, originally known as Pragostimine, was an illegal chemical.
Bloom was developed on Earth in 2002 as a fertiliser. By 2010 it had been declared illegal under the First Reconstruction Act. Roz Forrester said that the act made "viral weapons illegal". By the 30th century it was known as Bloom and remained illegal. It could be used in the Kilbracken cloning technique, since it built flesh from DNA.
The Master used Bloom with the technique and the Loom of Rassilon's Mouse to try to create a new body for himself. He chose to do so in Cheldon Bonniface during the festivities surrounding the wedding of Bernice Summerfield and Jason Kane in 2010. (PROSE: Happy Endings)