"Blood" is the third episode of the second season of the science fiction television series The X-Files. It premiered on the Fox network on September 30, 1994. The teleplay was written by Glen Morgan and James Wong from a story by Darin Morgan, and was directed by David Nutter. The episode is a "Monster-of-the-Week" story, unconnected to the series' wider mythology. "Blood" earned a Nielsen household rating of 9.8, being watched by 8.7 million households in its initial broadcast. The episode received mostly positive reviews.

The second season of the science fiction television series The X-Files commenced airing on the Fox network in the United States on September 16, 1994, concluded on the same channel on May 19, 1995, after airing all 25 episodes. The series follows Federal Bureau of Investigation special agents Fox Mulder and Dana Scully, portrayed by David Duchovny and Gillian Anderson respectively, who investigate paranormal or supernatural cases, known as X-Files by the FBI.