The influence of several factors on the amount and availability of iron in uncooked turnip greens was studied. Plants were grown in nutrient solutions containing 59Fe, and iron availability was estimated by feeding homogenates of these 59Fe-labeled turnip tops to iron-depleted rats, then measuring retained 59Fe in a whole-body counter. Younger leaves generally had higher iron concentrations than older leaves, and increasing the iron concentration of the nutrient solution generally produced only a small increase in leaf-blade iron concentrations. Plants grown in nutrient solutions deficient in nitrogen, phosphorus, and potassium contained more iron than control plants, but the iron was less available to rats and was less soluble in a variety of extractants, including 0.2 N HCl. Iron from “intrinsically” labeled uncooked turnip green homogenates (plants grown in nutrient solution containing 59Fe) was significantly less available than that from “extrinsically” labeled homogenates (59FeCl3 added directly to the homogenate). In these studies, the “extrinsic tag approach” would have overestimated iron availability.