Blood Brotherhood

 refers to an unmarked and repeatable quest in the Fallout 3 add-on Broken Steel.

Walkthrough
After the completion of Who Dares Wins, Paladin Tristan asks you to kill Super Mutants and bring back Super Mutant Blood Samples so the Brotherhood could research a weapon that could destroy Super Mutants with ease. These samples can be found on any super mutant you kill, and can be exchanged with Paladin Tristan in the Citadel's A-Ring for caps and XP.

Reward

 * 50 caps and 10 XP per blood sample