The lead content of roadside and playground dust in urban areas is frequently high enough to make a major contribution to the lead intake of children through accidental ingestion of the dust. The question arises as to whether the material presents the potential toxic hazard suggested by its gross lead content. Although the fact of the build-up of lead from aerial deposition in surroundings frequently washed by rainwater suggests rather low lead solubility, the acidity of stomach fluids is much greater than that of rainwater, giving the possibility of a marked difference in solubility. We now report measurements of the extractability of lead at various acidities, our object being to assess the potential toxicity, following ingestion, of this form of environmental lead.