A body of preclinical data has provided a strong rationale for evaluating the combination of IFN-alpha with retinoic acid. The two drugs have different mechanisms of action and, when used in combination, show enhanced activity in both adult and pediatric tumor cell lines. In the pediatric phase I trial which administered ATRA for 3 consecutive days/week repeated weekly, the AUC of ATRA decreased on day 1 to day 3 of drug administration but returned to day 1 levels at the beginning of subsequent weeks. This intermittent schedule of ATRA administration allowed for exposure to relatively high plasma concentrations of ATRA on a repetitive basis. The combination of ATRA/IFN-alpha 2a has demonstrated clinical activity in the pediatric phase I trial in neuroblastoma and Wilms' tumor. The combination of the antiproliferative and differentiation inducing effect of retinoids together with the antiproliferative, immunostimulatory and differentiation-potentiating effects of IFN-alpha warrant clinical investigation of this combination for the treatment of refractory pediatric malignancies.