The K-Ar-ages of Bediasites and Moldavites have been measured to be 29,4 and 8,7 · 106 years, while tektites from different localities between Indochina and Australia gave within the experimental errors concordant ages of 610 000 years. These results agree with the ages of the formations on which tektites have lain. The contribution of this work to theories about the origin of tektites is discussed.