The Symposium on the Use of Isotopes in Hydrology was organized by the International Atomic Energy Agency in cooperation with the United Nations Educational, Scientific and Cultural Organization. It was attended by 221 participants representing 44 countries. A total of 54 papers were presented.
The growth of the uses of isotopes in hydrology can be illustrated by the expansion since the first symposium which was held by the IAEA in Tokyo in 1963. Ninety-five participants representing 13 countries heard 27 papers presented. The second symposium, held in Vienna in 1966, was attended by 164 participants from 37 countries. Forty-one papers were presented.