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Principles of assessing body composition with bioelectric meth­ods and associated problems are discussed in the context of the papers presented at the symposium. Bioelectric impedance methods have the ad­vantages of convenience, rapidity and non-invasiveness, which have appeal for large scale surveys. Prediction equations derived from impedance analy­ses have standard errors of estimate that are reasonably similar to those derived from more traditional methods of body composition assessment, although there appear to be systematic errors at the extremes of relative fatness. However, methodological limitations and biological interpretation of results of bioelectric impedance and total body electrical conductance analyses need to be refined in both the general population and special groups such as the obese and those with various clinical conditions. The available data are derived primarily from White adults with little informa­tion on developing individuals and other racial groups. There is also a need to analyze further the effects of factors that may influence the electrolyte content of lean tissue, e.g., specific dietary components, bouts of acute physical activity, and certain disease states.