Of the thousands of chemicals tested, the only compounds found to be potent carcinogens for the oesophagus are the N-nitrosamines. Many of these compounds are readily formed from common precursors in the environment (eg example in food during its storage or preparation) and also in vivo in the human stomach. Exposure is therefore likely to be ubiquitous. Although man may be exposed to other oesophageal carcinogens these have yet to be chemically identified, and at present nitrosamines are the sole contenders for the role of initiators of oesophageal cancer in man. Evidence suggests strongly that oesophageal cancer is initiated world-wide by nitrosamines, and promoted by secondary factors, the nature of which varies with the population concerned, notably alcohol in Europe and the USA, dietary deficiencies in China and Iran, mycotoxins in South Africa. When several risk factors coincide in one locality, the result can be a very high incidence of oesophageal cancer, with no one major cause.