Increase of the dosage of cellular oncogenes by DNA amplification is a frequent genetic alteration of cancer cells. The presence of amplified cellular oncogenes is usually signalled by conspicuous chromosomal abnormalities, "double minutes" (DMs) or "homogeneously staining chromsomal regions" (HSRs). Some human cancers carry a specific amplified oncogene at high incidence. In neuroblastomas the amplification of MYCN has been found associated with aggressively growing cancers and is an indicator for poor prognosis. MYCN amplification is of predictive value for identifying neuroblastoma patiens that require specific therapeutic regimens and for identifying patients that will not benefit from chemotherapy.