A prospective study was set up to test the hypotheses that the risk of death from various diseases is reduced by a high intake of dietary fiber or by vegetarianism. A simple screening questionnaire was distributed among persons with a special interest in health foods, and 10,943 subjects were recruited and followed-up. Their mortality was ascertained by flagging their National Health Service records, and analyzed after 7 yr. A significant negative association was found between vegetarianism and mortality from ischemic heart disease which was especially marked among the men and did not seem to be due to a confounding effect of smoking. No significant associations were found with fiber, although persons who habitually ate wholemeal bread had a lower mortality from cerebrovascular disease. These findings confirm other evidence of a lower mortality from heart disease among vegetarians.