Larry G. Hansen, a professor emeritus in the department of veterinary biosciences, University of Illinois, Urbana-Champaign, is the author of The Ortho Side of PCBs: Occurrence and Disposition. Larry W. Robertson is a professor in the department of occupational and environmental health and director of the interdisciplinary graduate program in human toxicology at the University of Iowa. He is coeditor (with Hansen) of PCBs: Recent Advances in Environmental Toxicology and Health Effects.