We have assessed the possibility that rare allelic variants of the c-Ha-ras-1 locus may be linked to a susceptibility to malignancy [1]. c-Ha-ras-1 genotypes were scored in 41 patients with myelodysplasia (MDS), 51 patients with acute myeloid leukaemia (AML) and 52 normal subjects. The incidence of rare alleles in the MDS patients was 4.8% and in AML an incidence of 15.7% was found. No rare alleles were found in the normal subjects. We conclude that rare alleles in MDS are not a common predisposing factor.