We analysed DNA from 68 neuroblastoma tumours for loss of heterozygosity (LOH) on the distal chromosome 1p (1p-LOH) using PCR-based DNA polymorphisms. Fifteen tumours (22%) displayed 1p-LOH. The shortest region of overlap (SRO) for the deletions was defined proximally by marker D1S244 and distally by marker D1S80. The CDC2L1 locus, located on chromosome 1p36, has been put forward as a neuroblastoma tumour suppressor. We analysed coding regions of the CDC2L1 gene in a subset of aggressive neuroblastoma tumours with known allelic loss for different 1p-markers. Single-stranded conformation polymorphism, heteroduplex and sequencing analysis of tumour DNA did not reveal any significant changes in the coding region. Using a DNA sequence polymorphism, we showed, in a primary tumour with an interstitial allelic deletion, that this tumour had both alleles of the CDC2L1 locus retained in the tumour. Thus, we showed that the neuroblastoma tumour suppressor critical region on 1p in our material is defined by loci D1S244 and D1S80 and that the CDC2L1 locus is distal to the critical region.