Caecal fermentation in rats fed diets with 40% autoclaved potato tubers was examined. The potato tubers of the conventional cultivar, Irga, somaclone Irga, and four transgenic lines with genetically improved resistance to a necrotic strain of potato virus Y (PVY^N) were compared. As regards the analysed indices, tubers of transgenic clone R1F (truncated gene coding PVY^N polymerase in sense orientation), R2P (truncated gene coding PVY^N polymerase in antisense orientation), and NTR1.16 (non-translated regions of the PVY^N genome in sense orientation) were similar to tubers of the conventional cultivar Irga. Tubers of transgenic clone NTR2.27 (non-translated regions of PVY^N genome in antisense orientation) increased the amount of caecal digesta and production of SCFA compared with tubers of the conventional cultivar and other transgenic clones.