The tolerance of tetraploid wild wheat Aegilops L. (Ae. biuncialis; Ae. cylindrica) species and cultivated wheat Triticum durum L. (cv. Firat-93; Harran-95) cultivars grown in Turkey to freezing was investigated by regrowth experiments and cold and freezing protein analyses. The results of the regrowth experiment showed that the seedling shoot length of genotypes decreased significantly when the duration of freezing time was increased from 3 to 24 h, compared to the untreated seedling at the end of the regrowth period, but increased when the regrowth period was increased from 24 to 72 h, at -5 +/- 1 degreesC. At -7 +/- 1 degreesC, none of the genotypes survived after 6, 12, and 24 h freezing periods, but did survive after 3 It. Although all the genotypes showed a tolerance greater than 50% at -5 +/- 1 degreesC for 3 h, wild wheats were found to be more tolerant than the cultivated wheats. On the other hand, during -7 +/- 1 degreesC freezing treatments, only Ae. biuncialis was tolerant for 3 h, while the other genotypes were sensitive to all the periods. The results of electrophoretic patterns of soluble shoot proteins showed that cold acclimation and cold acclimation plus freezing conditions induced two separate groups of proteins. In the first group, only one protein (67 kDa pI 5.7) was induced in both genotypes. This protein may not be associated with development of freezing and may have resulted from growth at low temperature. In the second group, new proteins were synthesized in tolerant Ae. biuncialis (66-22 kDa pI 7.5-5.5) in higher amounts than in sensitive Harran-95 (66-42 kDa pI 7.3-5.7). The proteins newly synthesized under these conditions may be associated with the cold resistance capacity of such genotypes. Also, a 50 kDa pI 6.4 protein was induced in the tolerant genotype. These proteins may play an important role in cellular adaptation to freezing.