I.C. Guță, E.C. Buciumeanu and L.M. CiripanGrapevine virus diseases are widely spread in all viticultural areas of the world and they are considered detrimental, their presence is the most limiting factor of plants performances and vineyard life lasting. A large number of viruses have been identified in grapevine. From them, reported for the first time in 2012, Grapevine Pinot gris virus (GPGV) is spread all over the world. This study brings new knowledge about the virus distribution in plants throughout one year, the organ and period of sampling, for a reliable diagnostic. Additionally, the influence of high temperature on the physiological processes was investigated. Plants belonging to the 'Negru mare' genotype, natural infected with GPGV and Grapevine fleck virus (GFkV), maintained in a greenhouse, constituted the biological material. ELISA analyses of different grapevine organs and tissues (apex, leaf blade, petiole, young shoot, tendril, inflorescence, cane) located along the length of the shoot, carried out on different phenophases (before flowering, after flowering, veraison, dormancy) revealed that the conductive tissue was the most appropriate for diagnosis in the active growth period when the air temperature did not exceed 30°C. The measurement of the leaf temperature in two moments of the day (morning and afternoon), when the air temperature records increasing values revealed that at high temperatures (above 37°C), as a result of the intensification of the transpiration processes, the temperature at the leaf level does not increase progressively with the air temperature. Measurements of stomatal opening in two periods of the day in infected and virus-free grapevines showed that GPGV+GFkV complex infection caused sometimes a significant increase in stomatal opening both in the morning and in the afternoon, which could be a deficiency in the management of water and gas exchanges in plants.