Abstract: A method was described for determining As in organo-arsenic drugs; it was based on iodometric determination of pentavalent arsenic resulting from destruction by the rapid wet-oxidation method. The results obtained by the above method were in good agreement with the standard method described in the literature, but sodium cacodylate could not be decomposed by this method. The characteristics of the solution of potassium permanganate in sulphuric acid in the destruction of organic matter were tested. It was suggested that the content of potassium permanganate in sulphuric acid was not more than 7 per cent.