In 1974 the World Health Organisation (WHO) and United Nations Environment Programme (UNEP) jointly established a programme, known as GEMS/AIR, to monitor and assess urban air quality on a global scale. GEMS/AIR is a component of the United Nations Global Environment Monitoring System. GEMS/AIR is now being re-oriented with the new objective of providing the comprehensive information needed for rational air quality management. The programme will expand its geographical coverage, with an emphasis on developing countries, improve data quality, increase its use of other data (meteorological, traffic statistics, production statistics, etc.), and increase the use of data from other sources. The newly formulated objectives of GEMS/AIR are designed to help cities to obtain and interpret the information needed for developing abatement strategies. Strictly defined and implemented quality assurance and quality control procedures will play a central role in ensuring the comparability and compatibility of data obtained in the network. These proposals were endorsed during a meeting of Government-designated experts held in Geneva in November 1991.