[en] In 1973 the National Bureau of Standards (NBS) distributed three calibrated test solutions to interested laboratories. Two of these solutions each contained nine gamma-emitting radionuclides that the participants were asked to identify and quantify. The third solution contained ⁸⁹Sr and ⁹⁰Sr-⁹⁰Y, and participants were asked to perform a quantitative radioactivity analysis of the mixture. The results reported by all of the participating laboratories are given here. Most of the activity values reported for the mixed gamma-emitting solutions were within plus or minus 20 percent of the corresponding NBS values, but less than half of the laboratories reported ⁸⁹Sr and ⁹⁰Y activity values both of which were within plus or minus percent of the NBS values