A chemical X-ray method is proposed for determining trace amounts of arsenic and selenium in steel. The method utilizes a prechemical separation from the iron matrix and concentration of arsenic and selenium on a micrôpore membrane by reduction to the free metal by tin(II). Selenium was found to be a suitable carrier for arsenic (300 mug of selenium for the quantitative precipitation of 10-200 mug of arsenic). Arsenic (300 mug) was found to be a suitable carrier for up to 200 mug of selenium. Up to 200 mug of tellurium and antimony were experimentally found not to be co-precipitated with either arsenic or selenium.