Objectives: The aim of this study was to examine the mutagenic properties of two new monomethine cyanine derivatives and to determine whether the difference in their chemical structure affects the ability to induce mutations. Study design: The study was an experimental research. Material and Methods: The producer of materials was MOLTOX, Boone (USA) and Acros Organics, Geel (Belgium). DMSO and were used as a negative control and (sodium azide) dissolved in sterile distilled water at a concentration of M was used as a positive control. The tested compounds, MCD 4 and MCD 8 were prepared at concentrations of M. Incubation of bacterial cultures lasted 48h at 37 ° C. Ames mutagenicity test was performed according to the MOLTOX instruction without S9 enzyme activation system. Results: No test compound induces a significant increase in revertant bacterial colonies in any bacterial strain. Moreover, a smaller number of revertant colonies on the TA100 strain treated with MCD4 was recorded than for negative control, which is why it is concluded that it has a potentially bactericidal effect, but additional studies are needed. MCD 8 treatment leads to an increased number of revertant colonies compared to negative control. Conclusion: No mutagenic effect of MCD 4 and MCD 8 on TA1535 and WP2 strains was demonstrated. MCD 4 has a potentially bactericidal effect, and MCD 8 is susceptible to mutagenicity which needs to be further investigated. The action of MCD 4 and MCD 8 on Ta100 strain is likely to be due to the presence of plasmid pKM101 and the difference in the chemical structure of the tested compounds.