This paper describes the development and results of the metals component of the UNEP/WHO Pilot Project on Assessment of Human Exposure to Pollutants through Biological Monitoring. This project was carried out within the framework of the Global Environmental Monitoring System (GEMS). The project was initiated in 1978 following the recommendations from a UNEP/WHO meeting of a Government Expert Group on Health-Related Monitoring, held in Geneva in 1977. The immediate objectives were: a) to review and agree internationally on selected methods to be used for analysis and evaluation of levels of a limited number of pollutants in selected tissues and body fluids; b) to provide technical advice and arrange training programmes for scientists and technicians; c) to design and implement a programme for rigid quality control in connection with sampling, storage, transport and analysis of tissues and body fluids; and d) to carry out a number of pilot studies on selected segments of the population in a specified number of countries.