AbstractAn intercomparison of the absolute reflectance scales of NBS, Washington, D.C. (USA), NRC, Ottawa (Canada), and PTB, Braunschweig (FRG) was organized by sending two samples of Russian opal glass MS‐20 to the three laboratories. An additional exchange of a Halon sample between NBS and NRC was arranged. The results of this intercomparison are presented. They show that the three different geometries used at the three laboratories yield values which agree to within ±0.