Five winter wheat cultivars, 'El Tan', 'Froid', 'CDC Kestrel', 'Norstar', and 'Tiber', and the germplasm line Oregon Feed Wheat #5 (ORFW) were acclimated for five weeks at 4C, then frozen to a target temperature over a 6hr or 8hr period. The temperature was then gradually increased to 20C. The target temperatures had been previously determined to result in about 50% death of plants. Plants were grown in plastic packs with a temperature probe inserted such that the roots were within about 1cm of the temperature probe. Temperatures were recorded at 5min intervals. For regression analysis, the temperature profiles experienced by the plants from the time the soil temperature was lowered to 0C until it reached 0C again after freezing was analyzed to measure the following factors: rate of temperature decline, minimum temperature, minutes below 0C, minutes at the minimum temperature reached, and degree minutes, a measure of time below 0C multiplied by the time below 0C. Survival was scored after 4wks of regrowth in a greenhouse. Statistical analysis indicated there were differences among cultivars in the proportions of variance explained by the factors. These results suggested different mechanisms leading to freezing tolerance were active in the various cultivars.