AbstractThis paper is a Progress Report on the work of the Joint Committee of the Ministry of Agriculture and the Association of British Insecticide Manufacturers on the determination of total mercury in organo‐mercurials. Consideration of the methods available and of the various types of product which might be encountered led to trials of selected methods on suitable mixtures; from this experience, the Committee developed a relatively simple method involving reduction with zinc in glacial acetic acid, filtration, dissolution of the zinc amalgam in nitric acid, and titration with thiocyanate. With minor modifications, the method is applicable t o samples containing benzene hexachloride or chalk; a further modification to cover samples containing lead arsenate and/or Prussian Blue is under investigation. The method has given reliable results for common types of product, with and without benzene hexachloride, but further work is necessary to cover other possible additive