Polychlorinated biphenyls (PCBs) and dioxins have polluted the environment for about 50 years and parts of them have transferred to human being through food chain. Humans are already contaminated with chlorinated compounds at relatively high levels. Yusho PCB poisoning occurred at Northern Kyushu in 1968 and the patients have been suffering from various symptoms for 35 years. High concentrations of toxic PCBs and polychlorinated dibenzofurans in the patients have been very gradually decreased to the levels of only 2 to 6 times higher than those of normal persons. Typical Yusho symptoms of acneiform eruption, dermal pigmentation and increased eye discharge were very gradually recovered with lapse of several years. However, enzyme and/or hormone-mediated signs of high serum triglyceride, high serum thyroxin, immunoglobulin disorder and others are persistently maintained for more than 30 years. Recent tolerable daily intake of dioxins were determined from their hormone-like activities, such as decreased sperm count, immune suppression, increased genital malformation and neurobehavioral effects in the offspring of animals. PCBs are important factors on considering dioxin toxicities to human for the reason that half the dioxin toxicity in normal persons consists of the toxicity of coplanar PCBs. Recent epidemiological studies have reported that higher levels of PCBs and related compounds in the human body associated with various health effects, such as lowering intelligence quotient levels, disorder of thyroid gland, higher rate of endometriosis in women, declining thyroid hormone levels, higher rate of diabetes in pregnant women, lowering age at menarche, and altering play behavior in children at school age.