The aim of the present work was to investigate interaction of iron-based powders with model biomedia in experiments in vitro. Objects to be investigated were nanosized powders obtained by reduction of iron oxalates under various process parameters. As a reference sample, extra-purity carbonyl iron was used. The reference carbonyl iron practically contains α-iron only. The powders produced from oxalates at 400-450 оС were composed of magnetite, which corresponded to the content of total iron ~65 mass%. The powders obtained by reduction of oxalates interact with all the model media 2-3 times weaker than carbonyl iron powder, except for the interaction of the powder obtained by reduction of oxalates in a of hydrogen medium with blood plasma. In the latter case, the quantity of the removed iron ions doubles that after interaction of carbonyl iron with the same medium. Therefore, the finer powder containing α-Fe, the more rapid its dissolution in blood plasma. All of the powders studied interact with the media containing human blood plasma more intensely than with the water media. The investigations carried out make it possible to draw a conclusion that processes in media containing blood plasma differ from those in water media: in the latter corrosion processes take place whereas in the former biotransformation occurs. This indicates that to understand processes in living organism, the use of media containing blood plasma is preferable in experiments in vitro. The rate of powder dissolution in blood plasma depends on the α-iron content and powder dispersity: the higher these parameters, the more intense process of powder transformation. Fe3O4 powders are resistant enough to the action of the model biomedia. The probability of organism intoxication upon using them is lower compared to carbonyl iron powders.