Overuse of immunosuppressive drugs in the treatment of renal transplant patients can cause the phenomenon of viral infection, especially EBV (Epstein Barr Virus) and BKV (polyoma BK virus), virus have no specific drug to treat. This research was done to study the EBV and BK virus PCR as guidline to reduce immunosuppressive drugs in 96 children with renal transplantation in Children hospital in Toulouse, France from 01/01/1998 to 31/12/2005. Results showed that the average time of BKV infection (7 months) was shorter than EBV (37 months). When patients with symptomatic or asymptomatic EBV infection, EBV PCR (-) respond very well with stop or reducing of anticalcineurine and have no stable renal function without acute rejection. When patients with symptomatic BKV infection, BKV PCR (-) respond very well with stop or reducing of anticalcineurine and have no stable renal function without acute rejection. In conclusion, monitoring of virus PCR is necessary in children renal transplantation. Virus PCR allows early viral detection and allows reducing doses of immunosuppressive drugs. Immunosuppressive drugs reducing can prevent and/or cure EBV and BKV virus infection without acute rejection.