Iron metabolism of microorganisms represents a good target for antibacterial and antifungal treatment. Because of its similarities with iron and disability of biological systems to differentiate them, metal gallium is a potential inhibitor of iron-dependent metabolic pathways. A „Trojan Horse“ concept implies using antimicrobial agents which microorganisms consider as iron source and they actively transport them inside a cell. Example of such compounds are hydrazones and aroylhydrazones, substances with known antimicrobial activity and ability to chelate iron and gallium. Gallium and hydrazone complexes are more stable and more bioavailabilable than gallium itself. At the same time, they represent a combination of two substances with known antimicrobial acitivity in one compound. Of thirteen newly synthesized aroylhydrazone complexes (derived from salicyaldehide and nicotinic acid hydrazide) with iron and gallium, only gallium complexes showed in vitro antimicrobial activity on tested S. aureus, E. coli and C. albicans strains when using agar-well diffusion method. IC50 and IC90 (MIC) values were determined with broth dilution for compuonds 1 – 13. Compuond 5 (MIC equals 59,60 μg/mL for E. coli ATCC 10536 and 111,2 μg/mL for ESBL+ E. coli MFBF 12794), compound 6 (MIC equals 32,02 μg/mL for C. albicans ATCC 10231 and 64,62 μg/mL for C. albicansFLR+ MFBF 11100) and compund 7 (MIC equals 97,95 μg/mL for S. aureus ATCC 6538 and 109,1 μg/mL for MRSA MFBF 177) showed the best activity. „Time-kill“ assay showed that compound 6 expresses fungistatic activity at 2xMIC concentration during 24 hours on C. albicans ATCC 10231 and C. albicansFLR+ MFBF 11100 strains in vitro. Same complex reduced the logarithm of C. albicans ATCC cellular viability by 26,80% and C. albicansFLR+ viability by 30,12% after 24 hours incubation.