Yucheng ("oil-disease") victims were Taiwanese people exposed to polychlorinated biphenyls (PCBs) and their heat-degradation products, mainly polychlorinated dibenzofurans (PCDFs), from the ingestion of contaminated rice oil in 1978-1979. Serial studies in Yucheng offspring born between 1978 and 1992 are summarized. Children of the exposed women were born with retarded growth, with dysmorphic physical findings, and, during development, with delayed cognitive development, increased otitis media, and more behavioral problems than unexposed children. Recently, examination of the reproductive system has suggested that prenatal exposure exerts late effects on semen parameters in young men after puberty. Results of the investigation in Yucheng children will provide important information about the human health effects and toxicology of PCB/PCDF exposure. Prenatal exposure to these environmental chemicals causes the fetus to be sensitive to the toxic effects of persistent organic pollutants.