A compilation of 295 geochronological data of 52 alkaline occurrences from Southern Brazil and Eastern Paraguay is presented. These data, mostly available in previous publications, were recalculated, using the new decay constants recommended by STEIGER & JAEGER (1977) for the K-Ar method. The estimated analytical error of the age determined using experimental parameters is also indicated (COX & DALRYMPLE, 1967). This paper aims, specifically, at making ages published prior to 1977 compatible with recent data, allowing, for example, comparisons between ages obtained from a single alkaline massif or from neighbouring massifs. By calculating K-Ar ages using the constants recommended by STEIGER & JAEGER (op. cit.), there occurs an increase of 2.1 to 2.4% in the value of the age calculated with the previous constants
