While this study is larger than previous investigations and includes workers with a wide range of exposures to benzene, the estimates of risk, as measured by statistical confidence intervals, are still fairly broad, and would benefit from the larger numbers that could be provided by continued follow-up of this population. Nevertheless, the study confirms earlier findings of increased risk for ANLL and aplastic anemia among benzene-exposed workers, provides the first substantial evidence that MDS is linked to benzene exposure, and provides evidence that benzene increases risk for ANLL/MDS at lower levels of exposure than had previously been demonstrated. Currently we are evaluating the potential for extending the follow-up of workers included in this study. A new study would include expanded data collection for cases of hematopoietic malignancy and related disorders and for an appropriate control series.