To study the association between dietary fiber, beta-carotene and breast cancer, the average daily intake of these dietary components was compared among 133 incident breast cancer cases and 238 population controls. Average daily intake of cereal products, fruit and vegetables was also studied. A statistically significant lower energy-adjusted intake of dietary fiber was observed in cases than in controls (mean +/- SD: 25.4 +/- 6.7 g vs. 27.7 +/- 7.4 g, 95% confidence interval (CI) of the age-adjusted difference = -3.8, -0.8). Intake of beta-carotene was similar for cases and controls. The multivariate adjusted odds ratio (OR) of breast cancer among women in the highest quartile of intake of cereal products, as compared to those in the lowest quartile, was 0.42 (95% CI = 0.19-0.92) and the trend was statistically significant (p = 0.03). The corresponding OR for intake of dietary fiber was 0.55 (95% CI = 0.26-1.17) but the trend was not significant. The OR for the highest quartile of intake of beta-carotene, fruit, vegetables, and all vegetable products combined was less than unity, but there was no significant inverse trend. These results suggest that a high intake of cereal products, especially those rich in fiber, may be inversely related to incidence of breast cancer.