The correlation between N-myc gene amplification and heretofore known prognosis-associated factors was studied in 23 cases of neuroblastoma, comprising a total of 29 tumors (23 primary and six metastatic), examined in and after 1983. DNAs were extracted from tumor tissues preserved at -70 degrees C and digested with the restriction enzyme EcoRI. Southern blotting analysis was performed on these DNAs with the N-myc probe labelled with alpha-32P-dCTP. Prognosis-associated factors studied were age at diagnosis, stage, primary site, histological type, blood biochemistry tests, and catecholamine metabolites in urine. Amplification of N-myc gene was observed only in the cases in which primary site was the adrenal gland, but the relation to the stage, histological type, and prognosis was not as apparent as reported by other investigators. However, the amounts of catecholamine metabolites were low in the cases with amplification, and this suggests immaturity of catecholamine metabolism in the tumor with N-myc gene amplification.