[en] This report describes the design, production, and provisional certification of two new certified reference materials (CRMs): CRM No. 123 (1-7), U₃O₈ containing 18 trace elements, and CRM No. 124 (1-7), U₃O₈ containing 24 trace elements. The elements to be included and concentrations to be used were decided on the basis of information gathered from users of a previous CRM of this type, CRM No. 98 (1-7). The new CRMs were prepared by the addition of trace elements to high purity U₃O₈. Provisional certification was accomplished by an interlaboratory program in which four different laboratories analyzed the materials by carrier distillation dc arc emission spectrography