An investigation into the influence of genetic modification on potato tubers should include physical characte- ristics affecting their technological usability. Potato tubers of 15 clones of cultivar Irga transformed with viral genome sequences in order to improve their resistance to a necrotic strain of potato virus Y (PVYN) were examined. The mechanical properties of potato tubers were determined using a compression test and expressed by fracture stress, F(kPa); fracture strain, D (%); and Young modulus, E (kPa). The variability of F, D, and E for particular clones measured by standard deviations was extremely high. However, the influence of the modification type and breeding conditions appeared to be statistically significant but irregular during the three-year period of cultivation. While the effect of cultivation year was unmistakable, the order of F, D, and E values for the particular clones was not constant in the successive years. Results of detailed statistical analysis (variance and discrimination analyses) confirmed also a lack of stable tendencies in average values of the mechanical parameters for both groups and subgroups of clones representing the same modification model. No repeatable and statistically significant differences in F, D, and E were found, neither for the genetically modified nor for the control tubers. It can be concluded that the mechanical properties of potato tubers of cultivar Irga were not permanently affected by the type of genetic modification used.