We studied the elemental composition of autopsy tissue samples to characterize the trace element changes induced in various human tissues by uremia. Samples from the United States and Australia, including those from 120 uremic patients who had been on dialysis, 29 uremic patients who had not been on dialysis, and 64 control subjects, were analyzed by x-ray fluorescence. Tissues analyzed were aorta, bone, brain, heart, kidney, liver, lung, muscle, and spleen; elements measured included potassium, calcium, iron, copper, zinc, selenium, bromine, rubidium, strontium, molybdenum, cadmium, tin, and uranium. Uremic abnormalities that were statistically very significant were found, including increases of calcium, strontium, molybdenum, cadmium, and tin and decreases of potassium and rubidium. The distributions of iron, copper, and zinc are altered. We conclude that these abnormalities are primarily the result of the uremia and that, generally, they are neither greatly moderated nor exacerbated by the dialysis procedure.