In addition to a clinical study which investigated the bio-availability of three oral iron preparations S, L and X by using postabsorption serum iron concentration curves, the same drugs were compared in order to study their antianaemic efficacy, tolerance and drug costs arising during and iron therapy. Moreover, these iron drugs were related to other current clinical reports. Within all three iron preparations a very good correlation was found between bio-availability and haematopoietic efficacy: The very good absorbability of the bivalent quick release stick capsule preparation S (= 100%) corresponded with a very good capacity of haemoglobin regeneration (2,6 +/- 0,4 g Hb/1/day) whereas due to a very low absorbability (10% to 16%) the antianaemic efficacy of both iron(III) preparations L and X had to be rated as moderate to predominantly poor. In normal therapeutic dosis all three iron preparations showed no differences in tolerance. The ratio of side effects was similar to that after ingestion of placebo. In comparing the drug costs during a therapy leading to a real absorption of 1 g of iron the most effective iron(II)sulfate preparation S is 3.6 to 12.6 times cheaper than the compared trivalent preparations L and X. Therefore, there is no justification for the further production or introduction on the market of trivalent iron preparations.