A simple and rapid method for the determination of doxorubicin in plasma and urine by HPLC-EC is described. The method is accurate and precise and the limits of detection are 1 ng/ml for plasma and 10 ng/ml for urine. The method requires only l Ml of sample which is important in its application to clinical studies in infants and adolescents, since the amount of plasma is limited and a large number of samples are needed to define the pharmacokinetic parameters accurately. Both coulometric and amperometric were evaluated and the latter was preferred on the basis of detector selectivity. The methodology was applied to a pharmacokinetic study of doxorubicin given to patinets with osteogenic sarcoma. This study revealed that the disposition of doxorubicin in plasma and urine changes with repetitive dosing. Epidoxorubicin was used as an internal standard and the technique should be equally applicable to the analysis of this drug since the detector response and limits of detection were the same for both drugs.