- Retrieve experimental serum from institure.
This quest first become available during the main story quest The Glowing Sea, and if you choose to complete it, it must be complete before completing the Brotherhood misc. quest A Loose End. Virgil requests your help in obtaining a mysterious serum which can cure him of his affliction. Travel to The Institute (Location) to retrieve his serum and bring it back to him. If you wish to kill him during the quest A Loose End, giving him the serum may be a good idea because it makes for an easier fight.
Video guide to serum location