Essential trace metal status in obese (ob/ob) mice and their lean(+/+ and +/?) littermates was assessed by measuring the concentrations and total levels of Zn, Fe, Cu and Mn in several tissues. Data indicated that the concentrations of these metals were significantly lower in several tissues from obese mice at 22 weeks of age when compared to age-matched lean mice. In contrast, tissue concentrations and total levels of these micronutrients in obese and lean mice at 5 weeks of age were similar, indicating that altered trace metal status was a result of chronic obesity. These effects were independent of sex of the animal. Various characteristics of zinc metabolism in lean(+/?) and obese male mice at 10 weeks of age were also investigated. ⁶⁵Zn absorption was significantly higher in obese mice than in lean controls. This difference between phenotypes was not due to differential isotope dilution in either lumen or intestinal mucosa, response to overnight fasting, GI transit time, or hypertrophy of the GI tract. The turnover rate of subcutaneously administered ⁶⁵Zn was similar for obese and lean mice. Obese mice had significantly lower percentages of carcass ⁶⁵Zn and endogenous zinc present in skin, muscle, bone, spleen and testes, and higher amounts present in liver, small intestine and adipose tissue compared with lean mice. Constitutive levels of metallothionein were significantly different in several tissues of lean and obese mice. Together, these results demonstrate that chronic obesity alters tissue status of several micronutrients and zinc metabolism in ob/ob mice. / M.S.