Since 1967, a chemical plant in the town of Chapaevsk (Samara province, Russia) has produced large amounts of chlorinated compounds and is suspected to be a major source of local environmental dioxin contamination. Dioxins have been detected in the local air, soil, drinking water, vegetables, and cow's milk. Human exposure to dioxins is suspected as a factor in the deteriorating local public health. In an effort to characterize nonoccupational dioxin exposure among local residents, during the summer of 1998, 24 volunteers were recruited to donate blood and to provide information about their residence, employment, demographics, medical history, and dietary habits. Selected polychlorinated dibenzodioxins, dibenzofurans, and coplanar biphenyls were measured in blood serum samples. The mean concentration of total dioxin World Health Organization toxic equivalents (WHO-TEQ(98)) based on polychlorinated dibenzo-para-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (PCBs) was 61.2 (range 16.4-168.1) pg/g lipid. Subjects living in close proximity to the plant (less than 5 km) had significantly higher dioxin levels (mean WHO-TEQ(98), 75.7 pg/g lipid), as compared to subjects living more than 5 km from the plant (mean WHO-TEQ(98), 44.1 pg/g lipid) (P<0.04). Comparisons of the study results with available published data indicate that average blood dioxin levels were substantially higher in Chapaevsk residents than in nonoccupationally exposed populations of other parts of Russia, Europe, and North America. Chronic exposures of such magnitude may have appreciable adverse effects on public health.