SummaryThere is much evidence that nutrients can influence the outcome of studies of carcinogenesis in experimental animals. At present, much of the information is contradictory and of uncertain relevance to man. This is because different nutrients appear to affect different stages of the cancerous process and there may be many interactions between the nutrients, and between the nutrients and the cancer‐causing agents. It is unlikely that such agents will ever be entirely eliminated from the human diet but there is a real possibility that several classes of nutrients have a protective effec