A rapid quantitative method for As in biologic material, described, permits a batch for 6 detns. to Be completed in ca. 2 hrs. A mixture of HClO4 and HNO3 is used for destruction of organic matter. As is liberated as arsine in a fast stream of H absorbed in a few ml. of [image]/50 AgNO3 and directly titrated with [image]/495 I (1 ml. = 0.1 mg. AS2O3) to starch end-point in presence of sufficient excess of KI to keep Ag in soln. Micro-titration is regarded as superior to matching Gutzeit papers, the inherent error of which may operate indifferently over large and small real quantities of As. Recoveries of added As in amts. of 0.50-0.005 mgm. As2O3 compare favorably with recoveries by other methods. Duplicates are good and probably validity of results can be improved by conscious upward correction for consistent small losses.