A case-control study of the role of diet in the cause of breast cancer was conducted between 1988 and 1991 in Navarra, North Spain; 100 women with breast cancer and 100 hospital controls admitted during the same period were interviewed, using a food frequency-consumption questionnaire. Cases reported significantly lower consumption of fruits, vegetables and fish; relative risk (RR) for persons in the lowest tertile of consumers was: fruits, RR = 3.83, confidence limit (CL) = 9.12-1.66, P = 0.01; vegetables, RR = 1.92, CL = 4.57-0.80, P = 0.09; fish, RR = 0.32, CL = 6.31-0.83, P = 0.05. The risk increased for persons in the highest tertile of processed meat intake, RR = 3.20, P = 0.05. Nutrient intakes for individuals were estimated by multiplying the nutrient content of a selected typical portion size for each specified food item by the frequency that the food was used per month, and adding these estimates for all food items. Cases reported significantly less frequent consumption of vitamin C (ascorbic acid) and monounsaturated fatty acid; after controlling for total calorie intake, the RR was estimated for consumption of vitamin C (RR = 0.40, CL = 0.2-0.9), and monounsaturated fatty acid (RR = 0.30, CL = 0.1-1.08).