Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs and PCDFs) are released into the environment from the use of chemicals contaminated with PCDDs/PCDFs, the improper disposal of contaminated production wastes and incineration/other high-temperature processes. Certain congeners are extremely stable compounds which are persistent in the environment once released. An assessment is made of the sources of human exposure to one particular dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Representative values of 2,3,7,8-TCDD concentrations in the background environment and in man are selected from available data or, when not available, inferred from other relevant information. A pathway analysis is performed utilizing the exposure commitment method. Normal dietary intake of 2,3,7,8-TCDD is quite variable depending primarily on consumption of contaminated fish. Representative intake for the average adult of 0.1 ng day^-1 may be associated with a human body burden of 100 ng (∼ 7 ng 2,3,7,8-TCDD kg^-1 adipose tissues). The inferred biological half-time of this compound in the body is ∼5 years. The exposure evaluation also accounts for secondary pathways to man of 2,3,7,8-TCDD in air and drinking water. Estimates of transfer factors obtained from the repsenentative background levels should be generally relevant and may be applied to more specific cases of exposure.