Acidic blood is the ability to have blood with corrosive properties.
- Mary Krause was the only character known to have this ability.
Right after Rachel removed a tube administering a gas/drug through Mary's nasal cavity in Building 26, Mary woke up and began to stand. She was then shot by two guards and fell backwards. The gunshot splattered Mary's blood onto the sheets and flesh of another prisoner, and it burned thruogh that prisoner's sheets and flesh. The splattered blood burned like a strong acid or base. It is unknown as to whether Mary's blood is always acidic, but her ability seems to be passive as immediately after the tube was removed, and she was shot, her blood exhibited acidic properties.