In a clinical pilot study, performed as an intraindividual comparison, 3 oral iron preparations, one bivalent iron sulfate (quick release stick capsule preparation) and two trivalent iron citrate complex preparations with different additives, were investigated on 9 healthy young male test persons by the iron absorption test (postabsorption serum iron concentration curves) in order to study the bioavailability of these drugs and their compatibility. Whereas both iron drugs proved equally compatible when administered in therapeutical doses, it was again confirmed that the enteral bioavailability of the ferrous iron sulfate is superior to that of the ferric iron complex preparation. According to these results the medication of ferric iron preparations seems once again to be proved unsuitable, trivalent iron having first to be reduced to bivalent absorbable iron, there however being usually not enough "reducing capacity" in the gastrointestinal tract to do this.