PCBs have captured the attention of scientists, journalists and the public for three decades, but during most of that time attention was focused on a small number of the 209 possible chlorobiphenyls. Recent work has implicated many of the forgotten and/or unstudied congeners as neuro-endocrine active and potential developmental toxicants. This interest has created a need for information regarding the ‘non-dioxin-like' PCBs. The ortho Side of PCBs: Occurrence and Disposition integrates historical information, analytical interpretations, and global concepts with recent comprehensive residue reports and public health concerns. This condensed source of extensive information provides detailed comparisons of comprehensive data in a consistent format. The data will improve the accuracy of concepts regarding the occurrence and disposition of the 60-100 (rather than 6-10) most important congeners. Actual PCB burdens are shown to deviate from average steady-state profiles through sporadic exposures to unique mixtures characteristic of individual dietary sources. The task of accurate hazard characterization and risk assessment can be overwhelming, especially when sporadic changes are considered. Models and relationships are suggested to facilitate the efficient categorization and evaluation of the more important congeners.