Mammalian lignans such as enterolactone and enterodiol, which are produced in the colon from precursors in foods, have been suggested as playing a role in the cancer-protective effect of vegetarian diets. Despite this, very little is known regarding the amount that is produced from different food products. Therefore, the objective of this study was to determine the production of mammalian lignans from 68 common plant foods by using the technique of in vitro fermentation with human fecal microbiota, which simulates colonic fermentation. Results showed a wide range (21-67,541 microgram(s)/100 g sample) in the amount of lignans produced. On the average as a group, the oilseeds produced the highest amounts (20,461 +/- 12,685), followed by the dried seaweeds (900 +/- 247), whole legumes (562 +/- 211), cereal brans (486 +/- 90), legume hulls (371 +/- 52), whole grain cereals (359 +/- 81), vegetables (144 +/- 23), and fruits (84 +/- 22). The vegetables produced the second highest concentration of lignans (1,546 +/- 280) when the data were expressed on a moisture-free basis. Flaxseed flour and its defatted meal were the highest producers of lignans (mean 60,110 +/- 7,431). Lignan production with the in vitro method related well to the urinary lignan excretion observed in rats and humans. The data should be useful in the estimation of lignan production from a given diet and in the formulation of high-lignan-producing diet for the purpose of reducing the cancer risk.