A survey of international efforts from the partial test-ban Treaty (in atmosphere, in outer space and under water) in 1963 to the Soviet-USA negotiations on verification measures for the threshold test-ban Treaty is given. As was the case in the bilateral and trilateral negotiations, the question of adequate verification procedures has remained one of the major problems in the multilateral considerations on a comprehensive test ban. Over the years, a number of proposals have been made in order to solve the issue, in particular by Sweden and by the Soviet Union. In 1988, the four experimental data centres, situated in Canberra, Moscow, Stockholm and Washington, carried out separate and joint experiments in analysis methodology. Communication techniques between the four international data centres and a number of national seismological stations were also tested. In addition, a global data-gathering experiment was conducted, resulting in the creation of an initial research data base at the experimental data centre in Canberra. Further technical experiments are planned for 1989, and in 1990 a large-scale experiment in data exchange and analysis, involving up to a hundred seismological stations globally and lasting several months, is foreseen.