Recommendations for earlier planting of soybeans raise concerns about increased potential for seedling exposure to freezing temperatures. Previous studies indicate soybean seedlings are considerably more susceptible to freezing injury than are other legumes, such as clover and alfalfa. And there has been little evidence for genetic variability or capacity of soybean tissues to ‘harden' when plants are grown for short periods at near-freezing temperatures. Failure to avoid super-cooling of tissue water in these studies may have limited the capacity to identify genetic variation. Alternatively, soybean may not possess the physiological mechanisms to avoid or tolerate ice formation. We have observed no difference in tolerance to freezing temperatures, based on solute leakage from leaf tissues, in genotypes typical of the 1930s through 2000 even when experimental care is taken to avoid super-cooling. This result suggests that soybean may lack biochemical mechanisms necessary to tolerate membrane damage associated with ice formation. We are pursuing a molecular approach to test this possibility using soybean lines transformed with a tobacco MAP kinase kinase kinase (MAPKKK), which has been shown to improve frost tolerance in transformed maize seedlings.