'Rescue', 'Cadet', and the 42 reciprocal chromosome substitution lines derived from these two spring wheat cultivars were tested for vernalization response and cold hardiness. Cold hardiness was tested after hardening under a 16-h day for 8 weeks with 6 °C day and 4 °C night temperatures or in the dark for 7 weeks at 0.8 °C followed by 8 weeks at −5 °C. Chromosomes 5A, 5B, 7B, and possibly 2A carried loci for vernalization response. Chromosomes 2A, 5A, and 5B carried loci affecting cold hardiness measured after 8 weeks in the light at 6 °C during the day and 4 °C at night, whereas chromosomes 6A, 3B, 5B, and 5D were involved in cold hardiness after hardening in the dark at 0.8 °C followed by −5 °C. The results suggest that the rank order of cultivars for cold hardiness depends on the hardening technique used since the two different techniques tested had different genetic and presumably somewhat different biochemical bases.Key words: Triticum aestivum L., cold hardiness, vernalization.