The highly variable biological behaviour of neuroblastoma, a neoplasm which belongs to the family of primitive neuroectodermal tumours, is determined by its molecular pathological characteristics. Among them amplification of the N-myc gene is the most important factor in both therapeutic and prognostic points of view. Value of the amplification can be determined by different methods. The latest of them is the competitive polymerase chain reaction (PCR), essence of which is the parallel reaction of the target N-myc gene (exon 3.) and the endogen competitor CF gene (exon 3.) in the same reaction solution. The authors applied the method on 11 neuroblastoma cases diagnosed between 1994 and january of 1999. In three cases the amplification was determined also by fluorescens in situ hybridization (FISH). Six of the 11 cases were detected to have more than 10-fold, two of the six about 100-fold N-myc amplification. Results of the PCR and FISH correlated well. The two methods applied by the authors complete each other and are appropriate for determining the gene amplification which gives valuable prognostic and therapeutic information about the examined tumour.