Whether low-level benzene exposure produces health effects is controversial. We used routinely collected data from our medical/industrial hygiene system to study 387 workers with daily 8-hour time-weighted exposures averaging 0.55 ppm. The cross-sectional repeated survey design included 553 unexposed workers. Lymphopenia is considered to be the earliest and most sensitive indicator of benzene toxicity. We found no increase in the prevalence of lymphopenia among benzene-exposed workers (odds ratio, 0.6; 95% confidence interval, 0.2 to 1.8), taking into account smoking, age, and sex. There also was no increase in risk among workers exposed 5 or more years (odds ratio, 0.6; 95% confidence interval, 0.2 to 1.9). Examination of other measures of hematotoxicity, including mean corpuscular volume and counts of total white blood cells, red blood cells, hemoglobin, and platelets, produced similar results. We conclude that risk of lymphopenia and other early indicators of hematotoxicity are not increased among workers in this study who were exposed to low levels of benzene.