The role of diet on breast cancer risk was investigated in a case-control study of 345 patients diagnosed with primary breast carcinoma between 1986 and 1989 in the north-east of France (Lorraine). For each case, one control was matched for age (+/-3 years) and socio-economic status. The dietary history questionnaire consisted of a self-administered food frequency questionnaire, a 6-day food diary and an energy expenditure record. It also elicited personal characteristics and medical history. While taking into account total caloric intake and established risk factors, breast cancer risk was shown to decrease as consumption of fibre (p value for trend = 0.03), and garlic and onions (p value for trend <10(-6)) increased. This study also supports the epidemiologic evidence that saturated fat intake and breast cancer risk are associated in post-menopausal women (p value for trend = 0.03). Conversely, it suggests that unsaturated fat intake could lower the risk in the same subgroup (p value for trend = 0.03). Our findings on protective factors of breast cancer could induce effective preventive measures and warrant further experimental investigations to isolate specific subfractions.