POLLUTION of the environment has long been a subject of public concern and much attention has been paid recently to the new ecological factors introduced by the wide agricultural usage of pesticidal chemicals. Contamination of soil and crops has often featured in environmental studies of these pesticides, but so far little attention has been given to atmospheric pollution, although, as long ago as 1961, Harris and Lichtenstein1 showed that the loss by volatilization of aldrin, dieldrin, heptachlor and gammabenzene hexachloride was a major factor in their disappearance from soils treated with these compounds. Later, in the United States, the President's Science Advisory Committee drew attention to the fact that inhalation of air contaminated with pesticides might present a hazard to man2 and recommended that air should be continuously monitored for pesticide residue levels. In 1965, an Advisory Committee of the United States Food and Drug Administration referred to studies which showed the presence of up to 0.075 p.p.m. of dieldrin in total diets3 and considered the possibility that half as much again could be absorbed from “air or other exposures”.