In a number of human cancers genes capable of suppressing tumorigenicity have been identified and in some instances cloned. Successful isolation of such tumour suppressor genes has depended upon either the mapping of a locus which confers susceptibility to a specific tumour, or the finding of specific allele loss in the tumour cells of heterozygous individuals. In ovarian cancer it is known that a small proportion (approximately 5%) of tumours are due to inheritance (Lynch et al., 1989). However, as yet the locus responsible has not been mapped. The only incidence of allele loss in ovarian tumours reported is on the short arm of chromosome 11 using a c-Ha-ras I probe to detect an RFLP (Lee et al., 1989), and on 3p and 6 in a small number of cases (Ehlen & Dubeau (1990)). We describe here the results of analysis of 19 tumours for allele loss using a probe for a hypervariable locus on the long arm of chromosome 17. Approximately 77%(10/13) of tumours from informative patients showed complete or partial allele loss at this locus. Using a probe for the short arm of chromosome 17, 31%(4 of 13 informative patients) demonstrated allele loss at this position. These results suggest that possible involvement of more than one chromosomal locus in the development of ovarian cancer.