PHBs are found worldwide in all parts of the environment (soil, water, air), in wildlife, and in the human body (at measurable levels). Humans are mainly exposed to PHBs through contaminated food and to a lesser extent through inhalation and dermal absorption. The main sources of PHBs indoors are sealants, paints, floor sealants, ballasts in lighting fixtures, and contaminated dust. PHBs can migrate into surrounding materials, such as concrete or wood, and into indoor air. In the USA, indoor air concentrations of PHBs have been reported to be from five to 300 times higher than those in outdoor air, and that concentrations are higher in older buildings. In Europe, the highest indoor concentrations are found in buildings built between 1960 and 1975, sealed with elastic materials containing PHB. Mortality from cancer of the digestive tract has statistically significantly increased. Deaths from lymphoma cancer were on the rise, especially from Hodgkin’s disease in women. Men were at increased risk of mortality from biliary tract cancer and prostate cancer. Urinary metabolites for 2,3,4,7,8-pentachlorodibenzofuran are methoxy-pentaHDF and dimethoxy-pentachlorobiphenyl.