BACKGROUND Worldwide, 30% of the population, a greater proportion of whom are women and children, is iron deficient. Soybeans are a major source of nonheme iron in many human diets, but information on iron bioavailability is still conflicting. Because much of soybean iron is in ferritin [distinct from the poorly bioavailable iron in cereals resulting from interactions between calcium, Fe(III), phytate, and proteins in the meal], soybeans provide a target for manipulating seed iron composition to achieve increased iron bioavailability. OBJECTIVE The aim was to reevaluate soybean iron bioavailability. METHODS Eighteen women, most with marginal iron deficiency, consumed meals with intrinsically labeled ((55)Fe) soybeans (hydroponically grown and nonnodulating) as soup (n = 11) or muffins (n = 7) and a reference dose of (59)Fe as ferrous sulfate in ascorbate solution. The radioactivity in red cells was measured 14 and 28 d later. RESULTS The mean (55)Fe absorption from either soup or muffins was 27% and that from the reference dose was 61%. (55)Fe was distributed approximately equally between protein (49.3 +/- 3.0%) and phytate, a contrast with nodulating soybeans likely caused by a high phosphate content in the growth medium. There was an expected inverse correlation (r = -0.793, P < 0.001) between red cell radioactivity and serum ferritin concentration. CONCLUSIONS These results show that soybeans appear to be a good source of nutritional iron in marginally iron-deficient individuals. More study is needed on the effect of plant nodulation on the form of soybean iron, aimed at enhancing bioavailability to combat iron deficiency in at-risk populations.