Nature 401, 231– 232 (1999)

The average ratio of polychlorinated biphenyls (PCBs) to polychlorodibenzodioxins (PCDDs) or polychlorodibenzofurans (PCDFs) in samples of contaminated feedstuff, chicken meat and eggs (Fig. 1b) was incorrect as published (see fourth paragraph): the average ratio of PCB:PCDD/F was about 50,000:1 (not 22,000:1). The conclusions of our report are unchanged.