A method had been worked out for the determinotion of arsenic in tonics using the neutron radioactivation analysis technique. After irradiating the sample and the standard in a reactor with a flux of 1012 n/cm2/sec for two hours, it is extracted in dilute NaOH solution with heating to transform the arsenic into the soluble sodium arsenite and filtered. After adding arseniccarrier and dilute HCI to make the pH ±. 3, the arsenic is precipitated as As2S3 by H2S. The precipitate is weighed after washing with acetone and drying under an I.R. lamp, and the activity is analysed using a single channel gamma scintillation spectrometer in which a solid, 2 1/2 x 2 1/2 inch, Nal (Thallium activated) crystal served as the detector. The presence of Mn and Cu makes the analysis for arsenic rather high and in this case a further radiochemi cal separation has to be done.HITLER NATASUWARNA. POEY SENG BOUW dan DJALI AHIMSA;laboratori um Rodiopharmacy, Pusat Reaktor Atom Bandung.Penyelidikan ini dibantu dengan grant dari DURENAS.