It has been suggested that loss of heterozygosity (LOH) on the short arm of chromosome 1 is a critical event for the development of neuroblastoma, and we have previously shown frequent LOH on chromosome 14 in neuroblastoma. To pursue these observations, especially to define further the regions which are commonly deleted in the tumor, we examined for allelic losses in 27 cases of neuroblastomas by using a number of polymorphic DNA markers for chromosomes 14q and 1p. LOH was observed in 10 out of the 25 informative cases (40%) on chromosome 14q and in eight out of the 21 informative cases (38%) on 1p. The commonly deleted regions were distal to the D14S13 locus (14q32-qter) on chromosome 14 and distal to the D1S112 locus (1p36.1-pter) on chromosome 1. These results strongly suggest that tumor-suppressor genes important in the pathogenesis of human neuroblastoma are located on the distal part of both chromosomes 14q and 1p.