Neuroblastoma is a childhood neural crest tumour, genetically characterized by frequent deletions of the short arm of chromosome 1 and amplification of N-myc. Here we report the first evidence for a neuroblastoma tumour suppressor locus on 4pter. Cytogenetically we demonstrated rearrangements of 4p in 7 out of 26 evaluable tumours (27%). Subsequent analysis of loss of heterozygosity (LOH) by Southern blotting revealed allelic loss of 4p in 16/82 (19.5%) informative neuroblastomas. Taken together cytogenetic and Southern blot analyses showed loss of 4p in 20/86 neuroblastomas analysed (23%). The common deleted region was bordered by the probe D4S123 and encompassed the distal 34 cM of 4p. We found no evidence for genomic imprinting of the 4p locus as the 4p alleles lost in the tumours were of random maternal and paternal origin. LOH4p was found at all disease stages and in every age group. Furthermore LOH4p was present both in cases with and without LOH1p and amplification of N-myc.