CD (cluster of differentiation) markers may refer to a single molecule or group of molecules found on the surface of a cell that is highly specific to that particular cell. Because CD molecules are specific to a particular cell, they are often used to associate cells with certain immune functions or properties. CD molecules are routinely used as cell markers, allowing researchers to identify, estimate, and isolate leukocyte cell populations and lymphocyte subsets. They are mostly useful for classifying white blood cells and diagnosing lymphomas and leukemias.