The influence of a polymorphic variant of the ETS-1 oncogene on the predisposition to develop chronic B-cell leukemia (CLL) was investigated. A total of 59 patients with CLL and 59 controls were examined for the frequency of an XbaI restriction fragment length polymorphism RFLP of the ETS-1 oncogene which has been reported to occur more frequently in patients with hematological malignancies than in normal controls. We found no significant difference in the allele frequency between the CLL patients and the normal controls. These data suggest that the presence of the XbaI RFLP is not associated with CLL.