The relation between 17 micronutrients and breast-cancer risk was analyzed in a case-control study conducted between 1993 and 1999 in the Swiss Canton of Vaud. Cases were 289 women with incident, histologically confirmed breast cancer, and controls were 442 women admitted to the same hospital for a wide spectrum of acute non-neoplastic conditions unrelated to long-term modifications of diet. Dietary habits were investigated using a validated food-frequency questionnaire. Odds ratios (ORs) were obtained after allowance for age, education, parity, menopausal status, body mass index, total energy intake and alcohol drinking. For several micronutrients, the ORs tended to decline with increasing tertile of intake, with significant inverse trends in risk for potassium (OR for the highest tertile = 0.21), total carotenoids (OR = 0.42), lycopene (OR = 0.43), folic acid (OR = 0.45), vitamin C (OR = 0.19), vitamin E (OR = 0.37) and vitamin B(6) (OR = 0.54). In a model including a continuous term for the 7 micronutrients significantly related to breast cancer, the only persisting significant inverse relations were for vitamin C (OR = 0.23) and lycopene (OR = 0.64).