Sienna Guillory was offered the chance to reprise her role as Jill Valentine from Resident Evil: Apocalypse (2004), but had to turn it down due to scheduling conflicts with Eragon (2006) and the character was then written out of this sequel.
The possibility of a third film in the franchise was first discussed when Resident Evil: Apocalypse (2004) opened at number 1 on the US box office, earning more than $23 million in its opening weekend.
The nightmares of Alice indicate that she has a mild psychic connection to her clones, since some of their memories are transferred into her subconscious. This element becomes important for the sequels.
The White Queen was originally planned to appear in the first film but was excised from the screenplay. She was supposed to be the Artificial Intelligence controlling the main headquarters of Umbrella and not just the "Hive".
Claire Redfield in the video games is in a never-ending search for her brother Chris. When the main plot of the film was planned, the original purpose of the trip to Alaska would be the reunion of Claire with her brother. The Chris Redfield subplot was scrapped and the voyage to Alaska was rescheduled as a simple quest for a safe haven.
There was much speculation that the well-known character from the video games, Leon Kennedy, would make a cameo and his role would expand in the upcoming fourth film. For a long time it was rumored that the known actor Jensen Ackles would be cast as Leon Kennedy, but this never happened.
The trademark double spiral-shaped injections (representing D.N.A.) now have two liquids instead of one. The one spiral contains the blue liquid (the T-virus) and the other one contains the green liquid (the antidote). The mixture is supposedly capable of bestowing the regenerative features of the T-virus but without succumbing to the atrocious side effects - mutation into an undead.
The original script included some flashback sequences depicting the trial in the International Court of Geneva. The Umbrella executives were convicted for the genocide but the hearing came to an abrupt end when an army of undead barged into the courtroom.
Raccoon City is clearly Detroit, Michigan from the graphic about 6-7 minutes into the film. The Detroit river and Belle Isle are clearly discernible, as is the half moon shaped industrial park to the North (towards the left in the film).
The name of the terrifying mutation that Dr Isaacs morphs into during the final sequence is never mentioned in the film. The creature however is lifted directly from the video games and is called Tyrant. The complete name of the deadly virus is Tyrant virus. T-virus is just an abbreviation.
The original script implied that the reason for the global outbreak is that rats spread the infection. Apparently the fact that these rodents live mostly underground helped them survive. Although this subplot was discarded, there is still a shot of rats dwelling in the sewers of Tokyo in the final scene of the film.