The resistivity of graphene, a single atomic sheet of graphitic carbon, can be tuned by the presence of an external electric field and therefore has promise as a biological sensor. In traditional sensors, the sensing mechanism occurs only at the surface but measurements are made throughout the bulk. Because graphene field-effect transistors (GFETs) are only one atom thick, devices made from graphene have the potential to be more sensitive than traditional biological sensors. In this talk I will report on recent experiments demonstrating that GFETs can detect the metabolic activity of bacteria. Furthermore, I will report on progress to define noise sources and improve the signal-to-noise ratio of these sensors.