We studied the influence of highly dispersed elemental iron preparations on the productivity and metabolism of broiler chicks. Iron nanoparticles were synthesized using high-temperature condensation. No toxicity of the nanoparticles and their agglomerates was observed in an experiment utilizing a genetically engineered luminescent strain of Escherichia coli (K12 TG1). The efficiency of single intramuscular injections in 120 broiler chicks (Smena 7) of preparations containing iron particles with sizes of 80 ± 5 nm (nanoparticles), 923.7 ± 29.6 nm (nanoparticle agglomerates) or 9.8 ± 0.4 nm (microparticles) was compared. The use of these preparations increased the live weight of the chickens. The maximum difference in live weight was observed 4 days after the injection of nanoparticles (9.8%; P ≤ 0.01), 17 days after the injection of agglomerates (4.97%; P ≤ 0.01), and 17 days after the injection of microparticles (8.5%; P ≤ 0.01). Injections with iron preparations were accompanied by increased protein deposition, causing daily weight gain in chickens. This gain was higher by 1.3 -4.3 g when nanoparticles were used, by 0.6 -1.4 g for agglomerates, and by 0.1 -1.4 g for microparticles. The iron preparations promoted an increase in the arginine content of the chicken liver compared with that of control animals. After the use of nanoparticles, the arginine content increase was 2.25% (P ≤ 0.05) within 1 day and 3.78% (P ≤ 0.05) 7 days after injection. The arginine content increased by 2.08% (P ≤ 0.05) 7 days after the use of agglomerates and by 3.86% (P ≤ 0.05) 21 days after the use of microparticles. Thus, similar biological effects were shown for different sizes of elemental iron particles. These effects were enhanced as the particle size decreased, although further investigation is required before the joint use of metal nanoparticles and arginine.