This research was conducted in order to determine the vernalization periods of some winter wheat varieties improved and grown widely on transition regions of Turkey and having vernalization problems on some parts of these regions in some years. The research was carried out in outdoor conditions of Department of Field Crops, Faculty of Agriculture, Uludag University in Bursa. Bezostaja-1, Marmara-86 and Pehlivan varieties of winter wheat were used as plant material in the experiment. Seeds of the varieties were exposed to five vernalization periods (V0, V14, V28, V42 and V56 days). After vernalization, seeds were sown into pots on March 15 in each experiment year. In the experiment, parameters such as phyllochron, heading period and grain weight/spike were determined. According to the two-year results, V0 (control) and V14 did not affect the parameters (except phyllochron) in Bezostaja-1 and Pehlivan varieties. On the other hand, V0 did not have effect on the parameters (except phyllochron) of Marmara-86 variety. Varieties indicated differences in terms of the parameters determined in the experiment. The longer the vernalization period was, the shorter the phyllochron period and the heading period. In this study, grain weight/spike was used as criterion for determination of vernalization requirements of cultivars since this component is one of the most important components related to the seed yield. As a result, it was determined that Marmara-86 was less sensitive to cold treatment than other varieties and its proper vernalization requirement was 28 days (V28). The most suitable vernalization period for Bezostaja-1 and Pehlivan was found to be 42 days (V42). Attention must be paid when these cultivars are intended to be grown on cooler or warmer areas within or out of the transition regions. © 2008 Asian Network for Scientific Information.