A study appearing in Toxicology Science  [2001; 59(1):147-59] demonstrated that animals with elevated serum levels of dioxin and chemicals similar to dioxin had a high prevalence of endometriosis, and the severity of disease correlated with the serum concentration of the toxic chemical. Research appearing in Human Reproduction  [2005; 20(1):279-85 (ISSN: 0268-1161)] tested blood levels of PCBs in women with endometriosis and concluded that anti-estrogenic PCBs may be associated with the development of endometriosis. Research appearing in Fertility and Sterility  [2005; 84(2):305-12 (ISSN: 1556-5653)] also found a connection between the body burden of PCBs and similar chemicals to the incidence of endometriosis.