A WHO Task Group on Environmental Health Criteria for Nitrates, Nitrites and N-nitroso compounds met in Lyons from 16 to 20 February 1976. The Task Group reviewed and amended the second draft of the criteria document and made an evaluation of the health risks from exposure to these compounds. The preparation of the first draft of the criteria document was based on national reviews of health effects research on nitrates, nitrites, and N-nitroso compounds received from the national focal points for collaboration in the WHO Environmental Health Criteria Programme in Bulgaria, Canada, Czechoslovakia, the Federal Republic of Germany, Netherlands, New Zealand, Poland, the United Kingdom, the USA, and the USSR.