OBJECTIVES: The aim of our work was to evaluate effect of selected salicylamides on cell viability of sulfate-reducing bacterium Desulfovibrio piger Vib-7 isolated from the human large intestine, as well as to assess antimicrobial activity and biological properties of these compounds. METHODS: Microbiological, biochemical, biophysical methods, and statistical processing of the results were used. RESULTS: An antimicrobial activity and biological properties of salicylamides against intestinal sulfate-reducing bacteria was studied. Primary in vitro screening of the synthesized selected salicylamides was performed against D. piger Vib-7. Adding 0.37-1.10 µmol.L(-1) (N-(4-bromophenyl)-5-chloro-2-hydroxybenzamide, 5-chloro-2-hydroxy-N-[4-(trifluoromethyl)phenyl]benzamide, 5-chloro-N-(3,4-dichlorophenyl)-2-hydroxybenzamide, 5-chloro-2-hydroxy-N-(4-nitrophenyl)benzamide and 4-chloro-N-(3,4-dichlorophenyl)-2-hydroxybenzamide) caused decrease in biomass accumulation by 8-53, 64-66, 49-50, 82-90, 43-46% compared to control, respectively. The studied compounds completely inhibited the growth of D. piger Vib-7 under the effect of 30 µmol.L(-1). Moreover, addition of the compounds in the culture medium inhibited the process of dissimilation sulfate dose dependently. Treatment with salicylamides led to the bacterial growth inhibition which correlated with the level of inhibition of sulfate reduction. The data on relative survival of D. piger Vib-7 cells and cytotoxicity of salicylamides are consistent to our research in previous series of the biomass accumulation experiments. CONCLUSIONS: A significant cytotoxic activity under the influence of salicylamides was determined. These results are consistent with a data on bacterial growth and inhibition process of dissimilation sulfate. The strongest cytotoxic effect of the derivatives was observed in compounds of 5-chloro-2-hydroxy-N-[4-(trifluoromethyl)phenyl]benzamide and 5-chloro-2-hydroxy-N-(4-nitrophenyl)benzamide which showed low survival and high toxicity rates.