The Science Lab Key (理科室の鍵 Rika Shitsu no Kagi ) also known as simply Lab Key is an item found in Corpse Party, Corpse Party: Book of Shadows and Corpse Party: Blood Drive used to unlock the door to the Science Lab.
The Key itself is carried by Kensuke throughout most of the game.
The key becomes important if the player has inspected the Anatomical Model in the Science Lab as it is required to escape the room once the event starts.
It can be found in the bottom right hand corner of the Science Lab during the Event.
Corpse Party: Book of Shadows
Episode #2; 『Demise』
The Lab key is found after you try to use the Rusty Key to open the door in the reference room (You can only do that if you didn't pick up the Notebook in classroom 1-C earlier in the chapter, locking yourself to the wrong end route.) Yoshiki will ask Mayu to give him the key so he can scrape off the rust. After doing so, you will receive a new key and Nana will see a label on it, which says "Science-Lab - Staff only".
You will be able to use the key while being chased, using it will give you a Wrong End.