AbstractUrinary lignan and isoflavonoid excretion were examined in 11 men and 9 women consuming four nine‐day controlled experimental diets: basal (vegetable free), carotenoid vegetable (carrot and spinach), cruciferous vegetable (broccoli and cauliflower), and soy (tofu and textured vegetable protein product). Three‐day urine collections (Days 7–9) were analyzed for lignans and isoflavonoids with use of isotope‐dilution gas chromatography‐mass spectrometry. Urinary excretion of the lignans enterodiol and enterolactone was higher during the carotenoid and cruciferous vegetable diets than during the basal diet (p= 0.0001), suggesting that these vegetables may provide a source of mammalian lignan precursors. Urinary excretion of the isoflavonoids equol, O‐desmethylangolensin, daidzein, and genistein was higher when subjects consumed soy diets than when they consumed the other test diets (p<0.02). Gender differences in lignan excretion were observed. Men excreted more enterolactone (p= 0.006) and less enterodiol (p= 0.013) than women, implying a gender difference in colonic bacterial metabolism of lignans. There was no effect of gender on isoflavonoid excretion.