The concentration of the essential trace element Sn is elevated in several tissues of dialyzed uremic patients. Analysis of 80 postmortem liver samples from controls and nondialyzed uremic and dialyzed uremic patients shows that nondialyzed uremic patients also have abnormally high Sn concentrations, averaging about 3 times that of controls. These elevated Sn levels are associated with uremia rather than with dialysis. Abnormally high Sn levels are also found in the kidneys of uremic patients at autopsy. This may have special importance, since Sn is a powerful inducer of heme oxygenase activity in rat kidney. The urinary excretion of Sn by nondialyzed uremic patients is normal.