Studies on the loss of heterozygosity (LOH) in human malignancies have shown that a number of different chromosomal regions associated with putative tumor suppressor genes may be involved in any one given tumor. We have carried out a similar study on Wilms' tumor using a range of DNA markers for a number of tumor suppressor regions. We tested a total of 44 Wilms' tumors including material from bilateral cases and from patients with Beckwith-Wiedemann syndrome, Drash syndrome, Perlman syndrome, and hemihypertrophy. In 11 of 36 informative tumors we found LOH for markers for the short arm of chromosome 11; only one of these tumors had additional LOH for regions 5q and 17p. No LOH was found for regions 3p, 13q, and 22q. Thus our findings support a major role for chromosome 11p in Wilms' tumor development and apparent noninvolvement of other tumor suppressor genes. No correlation was found between allelic losses and the International Society of Paediatric Oncology tumor stage or histology.