The reproducibility of measures of the intake of total energy and 27 selected nutrients from a quantitative food frequency questionnaire (FFQ) used in a case-control study on cancer of the breast, ovary, and digestive tract was evaluated. The results of two FFQ administrations at an interval of 3 to 10 months (median = 5.4 months) to 452 volunteers (144 males and 308 females; median age = 50 years) from three Italian provinces (Pordenone, Genoa, and Forì) were compared. Pearson correlation coefficients (r) between crude nutrient intake (unadjusted for energy) ranged from 0.50 for vegetable fat to 0.80 for alcohol, with most values falling between 0.60 and 0.70 (median r = 0.67). Adjustment of nutrient intakes for total energy slightly decreased most coefficients (median r = 0.60). The agreement between the two measurements did not differ substantially by sex, age, education, and interval between interviews. The contribution of specific FFQ components (i.e., frequency-only questions, open questions, portion size, and fat intake pattern) was also assessed separately with respect to the performance and reproducibility of nutrient measures, yielding, in general, very similar results. The seven questions concerning individual fat intake pattern, which were used to modulate the composition of various recipes, led, however, to a significant increase in mean daily intake of vegetable fat, oleic acid, and vitamin E, but a reduction of estimated daily intake of linoleic acid and polyunsaturated fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)