Season four of Stargate SG-1, an American-Canadian television series, began airing on June 30, 2000 on Showtime. The fourth season concluded after 22 episodes on February 14, 2001 on British Sky One, which overtook Showtime in mid-season. The series was developed by Brad Wright and Jonathan Glassner. Season four regular cast members include Richard Dean Anderson, Michael Shanks, Amanda Tapping, Christopher Judge, and Don S. Davis.
O'Neill and Teal'c risk their lives to keep the Replicator bugs from gaining a foothold on Earth, while Carter helps the Asgard fend off a Replicator invasion.
A warring alien race offers to exchange their advanced technology for Earth's help in defeating their enemy.
A Tok'ra archaeologist arrives at the SGC with newly discovered technology, giving the SG-1 team superhuman powers.
Teal'c is reunited with his lost love -- a woman who claims to have found a way to communicate with her symbiote and defeat the Goa'uld.
When a member of the SGC tries to kill a Tok'ra, it is revealed that O'Neill and Carter may be victims of an untraceable form of Goa'uld mind control.
O'Neill and Teal'c are caught in a time loop in the SGC, and must relive the same 10 hours over and over again.
The Russians recover a Stargate from the bottom of the ocean, and turn to the SGC for help when their experiments go awry.
Dr. Jackson is taken captive by an Unas while on an archaeological dig. The SGC mounts a rescue operation, but discovers a danger of their own.
SG-1 is caught in a conflict between two civilizations trying to colonize the same planet.
The members of SG-1 are used as forced labor in an underground alien facility after their memories are erased by the ruling elite.
SG-1 investigates a conspiracy theorist who has detailed knowledge of the Stargate program.
A test gone wrong leaves Jack and Teal'c marooned in space aboard a damaged prototype attack ship
When his former mentor dies, Dr. Jackson returns to his roots -- and discovers an ancient Egyptian artifact containing a Goa'uld parasite.
SG-1 must stop Apophis and Heru-ur from forming an alliance of their powerful forces, while Teal'c is captured and tortured by the Goa'uld.
SG-1 must adjust to a new commanding officer when General Hammond steps down -- but O'Neill discovers foul play behind the general's resignation.
Ten years into the future, the former members of SG-1 must send a message into the past to prevent the extinction of the human race.
Jackson's teammates notice a disturbing change in him when he is reunited with the Harcesis child and given the Goa'uld genetic memory.
SG-1 finds a deserted Goa'uld palace, where a beautiful device causes suicidal tendencies.
Carter must help keep a promising young cadet from throwing away a future at the SGC. O'Neill and Teal'c encounter a dangerous life form at an offworld research base.
The SGC is invaded by an alien life force that takes up residence in the base computer system -- and in Major Carter.
SG-1 returns to Juna, formerly known as PX3-989, a planet they -- or rather, robot duplicates of them -- helped free from Goa'uld enslavement. Now the natives face the vengeful system lord Cronos. SG-1 is prepared to lead the planet's inhabitants against him, but the people are not eager to trust SG-1, who had told them that they would be safe from the Goa'uld if they buried their stargate.
SG-1 pays a visit to the Tok'ra homeworld. They arrive at Vorash on Cronos' mothership -- one of the spoils they claimed following the their recent battle with him. At a meeting with Vorash's High Council, it is revealed that SG-1 intends to lend the Tok'ra the enormous ship in order to help facilitate the Tok'ra's move to a new planet.