The article discussses the health effects of polychlorinated biphenyls (PCB). Between 1960 and 1977 Monsanto's Newport plant produced several types of PCB, that are persistent and ubiquitous and toxic. But their usefulness in industry made them too profitable to withdraw from the market until manufacturers were forced to do so by overwhelming evidence of their environmental persistence and toxicity to living things. Like all volatile chemicals they are also light, mobile and unseen. They move around the world quickly and settle in the fatty tissues of living organisms.