Аннотация:The biological impact of gold complexes AuPPh3Cl (1), PPh3AuSR (2) with a protective antioxidant group (R=3,5-di-tert-butyl-4-hydroxyphenyl) and RSH on reactive oxygen species (ROS) intensity in human colon carcinoma (HCT-116) was investigated. Intracellular ROS were detected with DCFH-DA. Mitochondrial superoxide radical-anion (O2 −˚ ) was detected with MitoSOX red. Quantitative fluorescence microscopy was performed in a wide-field fluorescence microscope Axioplan 2 imaging MOT equipped with digital camera and a mercury lamp. Obtained images were processed with AxioVision software . The AuPPh3Cl (1) complex is cytotoxic and initiates a diffuse increase in the level of ROS in the cells. MitoSOX revealed accumulation of O2 −˚ in mitochondria. It was shown that “green” and “red” mitochondria are colocаlized. The PPh3AuSR (2) complex with antioxidant R group is weakly cytotoxic. However, ROS significantly accumulate in intracellular structures, and not diffusely in the cytosol. The accumulation of O2 −˚ in the mitochondria is practically not observed.