Unique and uncommon BamHI allelic restriction fragments of the Ha-ras locus have been reported in the genomes of patients with cancer and of three affected members of a familial melanoma kindred (Krontiris et al., 1986). Analysis of the BamHI and Msp/HpaII restriction fragments of peripheral blood leucocyte DNA from the members of two families with hereditary melanoma (HM)/familial dysplastic naevus syndrome (DNS) revealed that the only Ha-ras allele common to four affected members of one kindred and two from a second kindred, was the 6.7kb allele which is found in 66% of the normal population. This allele was found equally in affected and non-affected family members, and in one affected case was inherited from an unaffected homozygous parent. It was absent in two affected sisters in a third kindred. In the first kindred the karyotype of all three melanoma sufferers was 46XX 9qh+, while six unaffected members had a normal karyotype. BamHI polymorphism of the Ha-ras gene does not identify the affected members in the HM/DNS families studied.