The influence of dietary factors, in particular the intake of fat and beta-carotene, on breast-cancer risk was evaluated in a case-control study including 1,486 breast cancer cases diagnosed over a 1 year period in Denmark. The control group was an age-stratified random sample of 1,336 women from the general population. Data on usual diet prior to the breast cancer diagnosis were collected by self-administered questionnaires of the semi-quantitative food frequency type. A highly significant trend (p less than 0.001) of increasing risk was observed with increasing fat intake, the RR for the highest quartile being 1.45 (95% Cl 1.17-1.80) compared with the lowest. However, information was not available to allow adjustment for the possible confounding effect of energy intake. The risk of breast cancer was not associated with consumption of vegetables rich in beta-carotene, multi-vitamin tablets or other dietary supplements, coffee, tea, sugar or artificial sweeteners.