The Food and Drug Administration has a continuing program of monitoring foods for their content of lead, cadmium, mercury, zinc, arsenic, and selenium to determine trends of increasing or decreasing levels. The monitoring protocol is that of the Total Diet Study, in which "market baskets" of typical foods and beverages consumed by 15- to 20-year-old American males are collected in various geographical locations at regular intervals during the year, divided into food classes, composited, and analyzed. Cadmium has the most widespread distribution of the six heavy metals and mercury the most limited. The analytical values for lead may be underestimated because of limitations of the methodology; these do not apply to the other five elements. A tabulation by year shows that the levels of these elements in foods do not vary significantly from one year to the next. Average intakes of lead, cadmium, and mercury are below the WHO/FAO tolerable intakes for adults; such tolerable intakes have not been established for arsenic and selenium. Increases in concentrations of these elements in foods would be considered undesirable, however.