In 1949, the first descriptions of human exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) contaminated chemicals were reported after a trichlorophenol reactor explosion in Nitro, West Virginia, USA. Reported non-cancer health effects included a range of conditions affecting most systems. Additional reports of the health consequences of exposure continued through the remainder of the century. The majority of effects have been reported among highly exposed groups including occupational populations, such as chemical production workers, pesticide applicators, and individuals who handled or were exposed to materials treated with 2,3,7,8-TCDD-contaminated pesticides, and among residents of communities contaminated with tainted waste oil (Missouri, USA) and industrial e uent (Seveso, Italy). For only six exposed populations were biological measurements of 2,3,7,8-TCDD contaminated collected and used to examine the relationship between non-cancer health effects and exposure. Of the many non-cancer health effects thought to be associated with 2,3,7,8-TCDD exposure, only chloracne, elevations in GGT and triglyceride levels, and alterations in FSH and LH were related to serum 2,3,7,8-TCDD levels. Mortality from cardiovascular diseases also appeared to be elevated among cohorts of exposed chemical workers and Seveso residents. Continued surveillance of the health of exposed populations will be useful in identifying the long-term effects of both high and low 2,3,7,8-TCDD exposure.