This study was the first reference sample containing arsenic, boron, selenium, and beryllium. Thirtyone agencies participated. It was designed at the request of Analytical Reference Service members who recognized a need for evaluation of current procedures and for comparison of individual laboratory results. It has been recognized that the presence of these trace elements in water have potential health and economic significance. The study served also as a survey of methods currently employed on a national basis. Each element in the sample was analyzed by a number of methods, permitting comparative evaluations.