This article demonstrates the need for indicators in the policy-making process and presents some of the current work on developing environmental indicators at the international, national and local levels. The paucity of indicators to demonstrate relationships between environment and health is outlined and a causal chain for physical pollutants--from source activity to emission, concentration and exposure--is presented. While indicators can be developed at each of these stages, indicators from earlier in the chain reflect processes which can more readily be controlled by policy; data is also more readily available for these indicators, yet only the later indicators are likely to provide a reliable guide to human exposure. A survey of 26 indicator projects from around the world yielded 8 sets which are in use and for which data exists. These were found to be only partially health-related and heavily weighted towards the source activity indicator category. Their utility as reliable indicators of human exposure is therefore seriously open to doubt and there is consequently a need to develop indicators specifically to assess environmental and health relationships.