This paper explores the many meanings attached to the designation,"the rodent in the laboratory" (rat or mouse). Generations of selective breeding have created these rodents. They now differ markedly from their wild progenitors, nonhuman animals associated with carrying all kinds of diseases.Through selective breeding, they have moved from the rats of the sewers to become standardized laboratory tools and (metaphorically) saviors of humans in the fight against disease. This paper sketches two intertwined strands of metaphors associated with laboratory rodents.The first focuses on the idea of medical/scientific progress; in this context, the paper looks at laboratory rodents often depicted (in advertising for laboratory products) as epitomizing medical triumph or serving as helpers or saviors. The second strand concerns the ambiguous status of the laboratory rodent who is both an animal (bites) and not an animal (data).The paper argues that, partly because of these ambiguous and multiple meanings, the rodent in the laboratory is doubly "othered"—first in the way that animals so often are made other to ourselves and then other in the relationship of the animal in the laboratory to other animals.