The hypothesis that lack of dietary fibre in the diet is responsible for a variety of large bowel problems, including cancer, has stimulated much discussion and research over the past 15 years. However, the epidemiological examination of this hypothesis has been hampered by the absence of data on the fibre content of most of the world's foods. In Scandinavia and Britain where the consumption of the major chemical fraction of dietary fibre, the non-starch polysaccharides has been measured using accurate methods, significant negative associations have been shown with large bowel cancer occurrence. These studies suggest that non-starch polysaccharides may be protective in populations at otherwise high risk of large bowel cancer from an excess of meat and fat. However, methodological problems in the assessment of non-starch polysaccharide consumption in individuals preclude the use of case control studies in verifying these associations within a single homogeneous population.