[en] Measurements on the radioactivity of aggregates for concrete making are parts of a greater project concerned with radioactivity determinations in building materials. The aim of this project is to study the variation of the radioactivity with different materials and with the places of origin of the materials. Outgoing from these data norms for allowed radioactivity in building materials could be formulated. Samples of aggregates have been obtained from 155 factories. Gamma spectroscopic analyses have been performed on 306 samples. A coarse sand, coarse gravel and mac-adam. The overall mean values of the activities of radium, thorium and potassium are 1.3, 1.9 and 22 pCi/g, respectively. Outgoing from these values the radiactivity in concrete is calculated. The geographical variations of the radioactivity are also discussed. (E.R.)