In the case of pre-malignant conditions it is often difficult to know when and whether a therapeutic intervention is necessary and a careful consideration of potential treatment-associated morbidity is indicated. Therapies have ranged from influencing the possible infectious etiology (by treating with acyclovir), decreasing the amount of immunosuppression (in transplant patients), to the use of immunomodulatory agents, including interferons and interleukins. Recent data have indicated that the use of differentiating agents, such as the retinoids, might offer yet another treatment option. In the current study we will try to get a better understanding of the pathogenesis and natural course of lymphoproliferative disorders in immunodeficient children.