We have examined the leachability of the toxic elements cadmium, arsenic, mercury, and selenium from solid wastes. The solid wastes studied are municipal incinerator ash, coal fly ash, hospital incinerator ash, raw sewage sludge, sewage incinerator bottom ash, and sewage incinerator lagoon ash (which is a combination of bottom and fly ashes). Cadmium displayed the greatest leachability in all waste types, with 76% leached from the municipal refuse incinerator ash. Although the sources of elements in the wastes are diverse, the leachability and hence the bioavailability in the incinerator ash appears mainly determined by the volatility of the element.