Test mutagenic serum on a super-mutant. Try Broken Hills

"Test mutagenic serum on a super-mutant. Try Broken Hills."

With Science at 80% or more, talk to Dr Henry. Asking about cyber-genetics gives a mission to inject a super mutant with a prototype serum. Use it on a super mutant. Observe data conclusively proving the appropriateness of scientists testing on lab rats first as the unfortunate test subject melts into a puddle of bones and goo. Gain 1000 xp. Return to Dr Henry and receive the option of adding a Cyberdog NPC to your party, subject to the normal party limit rules.

There are also super mutants in NCR, and notably in the Military Base.

The serum will work on both Elmo and Marcus in Broken Hills; obviously there are significant drawbacks to the latter. It will work on Gond and Lenny in NCR, and Grundel in the Military Base.

Bugs
Be aware that using serum in a duel with Lenny is buggy; it appears that once combat damage is done to Lenny, the serum will work and the fight will end, but if used at the beginning of battle, the game gets frozen permanently in combat mode.

If you use the serum on a super mutant in combat mode, you get the 1000 xp and complete the quest but the mutant will take one or a few turns before dying. If you kill it before then and loot the corpse the Mutagenic Serum may still be there.

If you talk to Cyberdog after reporting back, you can ask Dr Henry about cyber-genetics again and get the whole quest all over again.