Characteristics of drying injury and drying tolerance of corn (Zea mays L.) seed were investigated on the inbred lines A632, B73, and Mo17. Only minor injury occurred during the initial 4-24 hours of drying when ears were harvested at 48% and 38% seed moisture and dried at 50 C in a thin-layer drying system. Evaporation did not provide enough cooling to the seed to explain the injury lag. After the lag phase, germination dropped linearly with prolonged 50 C drying;Initial low-temperature drying (preconditioning) to 30-39% seed moisture rendered high moisture seed tolerant to subsequent high-temperature drying. Preconditioning may accelerate the maturation process normally occurring in the field. This result offers an opportunity for more effective seed corn drying and a challenge to explain drying tolerance. Moderate drying at 20 or 35 C resulted in more rapid and complete preconditioning of ear samples than storage at slow- or non-drying conditions. More moisture loss was required to obtain tolerance with slow field drying than with preconditioning at 35 C. Physiological factors other than moisture content are important criteria of high temperature tolerance. These so far unknown factors could be responsible for the change in drying susceptibility over years;Shelled seed samples could be safely dried at 35 C though samples dried more rapidly than with drying on the ear at 50 C. However, seed lost viability during 50 C drying much more rapidly when dried as shelled samples than when dried on the ear. Deterioration was reduced when ear samples were dried at 50 C and 60% relative humidity as compared with 50 C and 20% relative humidity. Thus both temperature and drying rate are factors in drying injury;Excised embryos germinated well in modified warm tests after being dried at 22-50 C even though excessive drying rates up to 40% per hour were observed. This high degree of drying tolerance suggests that embryos dried before injury could occur. However, embryo death in the cold test indicates that imbibitional chilling had been increased;Correlations between conductivity test values (indicators of membrane damage) and germination values were clearly significant. But the use of conductivity values to predict germination was not reliable except for Mo17.