To cope with cold stress, winter cereals regulate their development through adaptive mechanisms such as vernalization requirement. Eight wheat and four barley cultivars were planted to determine the relationship between vernalization fulfilment and expression of cold tolerance under both field and controlled conditions. Cultivars were planted at Maragheh and Karaj Agricultural Research Stations in Iran. Plants were grown at 4?C for vernalization periods from 7 to 98 days under controlled conditions. Cold tolerance, as measured by LT50, and vernalization requirement, as estimated from final leaf number (FLN), were determined during the vernalization periods. In cold region of Maragheh, the FLN measurements indicated that vernalization requirement was achieved between 11 to 12 weeks after planting for Noorstar and about 8 to 9 weeks for either of Azar 2 and Sardari winter wheat cultivars. Koohdasht spring wheat did not need to undergo the vernalization requirement. The minimum FLN for Dobrynia winter barley was observed about 8 weeks. Rihane-03 and Dicktoo barley proved to be of no vernalization requirements. In moderately cold area of Karaj, the vernalization saturation of Noorstar, Shahryar and Alvand winter wheat was achieved after about 15, 6 and 4 weeks, respectively. Kavir spring wheat needed no vernalization requirement. Under controlled conditions, the fulfillment of vernalization saturation was observed between 28 and 35 days for Azar 2, about 28 days for either of Sardari and Shahryar, and 21 days for Alvand wheat cultivars. The FLN of spring wheat (Kohdasht, Kavir and Zagros) did not change indicating that these cultivars did not need to undergo vernalization requirements. Similar to field conditions, Rihane-03 and Dicktoo spring barley were of no vernalization requirements, while Kold and Dobrynia winter barley cultivars met their vernalization requirements after between 28 to 35 days of vernlization treatment. Noorstar acclimated to a lower temperature reached its maximum cold tolerance (LT50=-21°C) at about the same time as vernalization fulfilment occurred (42-49 d). Under field conditions at Karaj, Noorstar reached the same level of LT50, which was obtained under controlled conditions, while Azar 2 reached LT50 of -10 °C at the vernalization saturation point. A similarity observed between vernalization in controlled conditions and that in field conditions indicates that fact that a fulfilment of vernalization is a turning point in cold resistence after which the resistance of plant to cold diminishes.