Many factors affect bioavailability of metals. Host factors can be defined as any attribute that can influence the amount and degree of metal exposure. In this series of articles, a wide range of aspects are discussed concerning the methodologies for assessing exposures to metals. These aspects include speciation, bioaccessibility, and bioavailability in the environment, in food, and in feed. This article complements the articles by Peakall and Burger and by Calderón et al., reviewing human host factors. In this article, measurement and assessment methods are discussed as they apply to risk assessment, with examples for arsenic, cadmium, chromium, and lead, as well as special consideration for source issues and children's risk. Finally, several examples from the current literature are cited to illustrate some of the approaches presently in use as well as areas of research that require further consideration, including longitudinal studies, as well as better biomonitoring and assessment strategies.