The title, "The Laboratory," may not seem like much, but it does a few different things in this poem. On the most basic level, it sets the scene. Even though the speaker of the poem never says it, we know from the beginning that this all takes place in a laboratory. On a broader level, we think it also helps Browning build up the mysterious, sinister mood of this poem.
We all know from famous books like Frankenstein that creepy stuff can happen in labs. It's not a spot for love and softness and tenderness, but for obsession and scheming. Sure enough, this lab has enough poison and smoke and dust and creepy old guys to be right at home in any horror movie. The title does its work by getting us ready for that.