In transplant recipients with CMV infection, the risk of developing CMV disease is directly proportional to the CMV DNA viral load. Historically at The Royal Free, Hampstead, patients were given preemptive therapy on the basis of two consecutive positive CMV PCR results as detected by a qualitative PCR technique. With the introduction of real time PCR, using a Taqman probe and the ABI7700 thermal cycler, it is possible to obtain rapid and sensitive results of viral load on clinical samples with a lower limit of detection of 200 copies/ml. Thus, viral load data can be incorporated into the clinical management of the patient.