Net photosynthetic rate (PN) and dark respiration rate (RD) were measured in Vitis vinifera L. cvs. Dimiat 4/24 (23rd subculture), Dimiat 4/38 (22nd subculture), and Italian Riesling 3/47 (22nd subculture) on days 3, 2, and 1 (1st series) before transfer from the in vitro culture and on days 14, 15, 16 (2nd series) and 28, 29, 30 (3rd series) after the transfer. PN of in vitro and ex vitro plants was strongly affected by irradiance. PN and RD of in vitro plantlets were lower and transpiration rate (E) was higher compared to those of ex vitro plantlets. PN, RD, and E changed in the course of acclimation. and T. Slavtcheva, V. Dimitrova.