We recently demonstrated an increased expression of fragile sites, induced by aphidicolin, in lymphocytes of neuroblastoma patients. We have now extended our studies to parents of affected children with neuroblastoma to verify if this characteristic may be genetically transmitted. We have examined 20 families. In most of them, the hypersensitivity to aphidicolin was found in the affected child and in at least one parent. Moreover, some of the parents showed an increase in the expression of the fragile sites 1p32, 1p13, or both that are preferentially expressed in neuroblastoma patients. The possible relations between the hypersensitivity to aphidicolin and the inheritance of predisposition to neuroblastoma must be clarified.