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The modified FEV is a quest item in Fallout 3. It is given to the Lone Wanderer by John Henry Eden in Raven Rock and can be inserted in the Auxiliary Filtration Input in Jefferson Memorial's Rotunda, contaminating the purifier's filter system and, subsequently, the Capital Wasteland's waters during the quest Take it Back!.


This vial contains a modified strain of the Forced Evolutionary Virus developed by President John Henry Eden, based on the earlier FEV Curling-13 strain used by the Enclave's Chemical Corps in 2241; intended to be placed into Project Purity's water purification system.[1] According to President Eden, the virus is designed to only target super mutants, ghouls, and all other "unclean" citizens, namely anyone who had been born in the Wastelands and exposed to radiation and other mutational effects from birth. The only people who would survive the infection are members of the Enclave and those who were born in the Vaults.[2] A vial of modified FEV is given to the Lone Wanderer by Eden in the hope that they will use it to contaminate Project Purity.


During the events of the add-on Broken Steel, if the player had chosen to contaminate the purifier with the modified FEV, what President Eden said is confirmed for as accurate and the FEV completely lethal. The medical facility of every city in the Capital Wasteland (except Tenpenny Tower and Paradise Falls) is filled with new patients dying from FEV infection. These new patients hold their stomachs and repeat dialogue along the lines of, "it burns on the inside." According to both Doctor Preston and Doctor Barrows, the FEV specifically targets the immune system of infected individuals, which in turn makes them vulnerable to other diseases. This occurs in both humans and ghouls, despite the latter's immunity to most diseases.[3][4] Along with affecting the immune system, the FEV severely weaken individuals both physically and mentally until it simply kills them.[5] The modified FEV is also completely undetectable by any kind of test meaning there's no possible way to screen water that has been infected as it only comes back as clean, purified water.[6]

The FEV is contained to only those that have ingested infected water as the transmission of FEV is impossible from physical contact or bodily fluids. In Rivet City, Dr. Preston comments that they are burning the corpses just to be safe.[3] The spread of FEV is contained to only bottles of Aqua Pura and the Tidal Basin for now. However, eventually, the spread of the FEV infected water will spread from the Tidal Basin and affect all water in the Capital Wasteland.

Related quests


  • With Broken Steel and if the Lone Wanderer drinks three successive bottles of Aqua Pura after having completed Project Impurity and inserting the modified FEV, it kills them.
  • It is not possible to leave the room where President Eden is located unless the Wanderer has picked up and retrieved the modified FEV from Eden's console.
  • This item uses the world model of an empty Nuka-Cola bottle as a placeholder, likely because, as a quest item, it can never be dropped normally.
  • It can be given to Elder Lyons for good Karma if he is spoken to after the escape from Raven Rock. With Broken Steel, it will be removed from inventory if Project Purity is activated without the FEV being given to Elder Lyons beforehand.
  • Should the player have completed the quest Project Impurity by infecting the water supply with modified FEV Curie III would've irradiated the water effectively neutralizing the virus.[7]



  1. The Lone Wanderer: "Where did this plan of yours come from?"
    John Henry Eden: "A great many years ago, the remnants of the government had a similar idea. I can only assume the plan failed, as I never heard word of its success. But the plan itself was sound. I've made a few modifications, and with your help, I do believe it can work. There's a bright future ahead of us, my young friend."
    (John Henry Eden's dialogue)
  2. The Lone Wanderer: "Won't this kill pretty much everyone in the Wasteland?"
    John Henry Eden: "Anyone or anything that has been affected by mutation will be eliminated. You will likely be immune, thanks to your upbringing in the vault. Likewise, the good people of the Enclave will be unaffected as well. I understand that you may have become sympathetic to certain individuals in your travels. Individuals this will eliminate. Please recognize that the fate of our entire country rests on this plan. Sacrifices must be made for the greater good."
    (John Henry Eden's dialogue)
  3. 3.0 3.1 The Lone Wanderer: "Doc, it's crowded in your clinic. Something going around I should worry about?"
    Doctor Preston: "Oh no... I'm fairly certain it's not contagious. Though, we are burning the bodies of the deceased, just in case... I just wish I knew how to treat these people. It's like their immune system is killing them. I don't know what to do about it!"
    (Preston's dialogue)
  4. The Lone Wanderer: "Doc, it's crowded in your clinic. Something going around I should worry about?"
    Doctor Barrows "I don't know yet. Some kind of virus that attacks the body on a cellular level. I've never seen anything like it. It's strange because ghouls are immune to almost any known disease."
    (Barrows' dialogue in Broken Steel)
  5. If the Lone Wanderer drinks four bottles of Aqua Pura infected with the modified FEV, they suffer increasingly negative effects (that are temporary) such as loss of strength and intelligence until the last bottle that kills them.
  6. The Lone Wanderer: "Doc, it's crowded in your clinic. Something going around I should worry about?"
    Doctor Church: "There's something going around, all right, but it isn't anything I've ever seen before. Definitely not contagious. Maybe something in the water, but that seems unlikely since I've tested it and this is the cleanest water we've ever had. I have no idea how to help these people and it's really taken the shine off my normally sunny disposition."
    (Church's dialogue)
  7. The Lone Wanderer: "How do you make your "holy water"?"
    Curie III: "It was a gift from Atom. I was meditating right here in Springvale, when four of His armored angels came to me. When I said I was from Megaton, they gave me barrels of "Aqua Pura," and said I should share it with my people. They were very clear on that. But when I shared some with my Enlightened brethren, it made them terribly ill. I questioned why Atom had brought a pestilence upon us. That's when I thought to consecrate it with Atom's Light. And lo and behold, it removed the pestilence and made the finest holy water imaginable!"
    (Curie III's dialogue) Note: This is the response given should the player have completed the quest Project Impurity by infecting the water supply with modified FEV.