The Lab is a room that appears for the first time in Luigi's Mansion. It is a lab inside Professor E. Gadd's lab, and is where the player starts every saved game. It is near Boo Woods, which is where Luigi's haunted mansion is. In this room, E. Gadd will ask the player where they want to go, the Mansion, the Training Room, the Gallery, and once the game is beaten, the Hidden Mansion. It is also where E. Gadd converses with Luigi in the beginning of the game. Luigi cannot move in this room, however.
- If the player looks in this room closely or uses the Game Boy Horror in the Training Room or the Gallery, they will notice that there is a wooden ladder visible, hinting that E. Gadd's headquarters is underground.
- With an Action Replay code you are allowed to walk around in E. Gadd's lab. You can't open the doors but you can climb the ladder that is next to E. Gadd, however. When you get to the top of the ladder, you go out of bounds, which is just an all black texture, which could mean that at some point in the games development, you would be able to walk outside of the mansion and possibly capture ghosts too.