N-myc amplification and ploïdic index are important prognosis factors in neuroblastoma. Combined overexpression of the multidrug resistance gene, MDR1 and of Glutathion-S-Transferase, GST-pi may be related to the response of tumors to chemotherapy. Measurements of these parameters may contribute to define responders and non-responders to chemotherapy and provide the clinician with additional criteria to manage treatment.