PREVIOUS studies of the presence of the persistent organochlorine pesticides in the atmospheric environment of this country1–3 have all indicated the need for more comprehensive surveys. The first of these studies by Wheatley and Hardman1 was confined to rainwater collected in the rural area of Wellesbourne, in Warwickshire. Subsequent studies by the Laboratory of the Government Chemist were concerned with the examination of rainwater2 and air3 collected chiefly in the central London area. These three studies showed that, in the areas concerned, the atmospheric environment contained small amounts of BHC, dieldrin and DDT; rainwater collected in these areas contained concentrations of up to 400 parts/1012 of these compounds and their breakdown products. The higher levels for DDT found in London rainwater, compared with that from Wellesbourne, were attributed to London air having a higher content of particulate matter, chiefly carbon particles, for which DDT has an affinity. Dieldrin probably also shows this affinity but to a lesser extent.