Hybrid maize (Zea mays L.) seed from desiccation-sensitive and desiccation-tolerant inbred lines B73 and A632, respectively, was harvested at moisture contents ranging from 500 to 400 g H2O kg-1 fw and preconditioned at 35°C for 0 to 48 h to study the effect of desiccation injury on axis mitochondrial function and chemical composition. Seed quality, as measured by the standard warm germination test and soil-free cold test, was high (>95%) for all drying treatments. Although not as great as previously observed, high-temperature (45°C) desiccation had a deleterious effect on seed vigor of both genotypes. A632 was somewhat more desiccation-tolerant than B73, as evidenced by higher shoot weights, and preconditioning at 35°C increased desiccation tolerance of both hybrids. Differences in seed vigor among genotypes and drying treatments could not be fully explained by changes in mitochondrial composition. The ratio of raffinose: sucrose in axis tissue was lower for B73 than for A632, primarily due to the higher sucrose content of B73. Phosphatidylserine (PS) composition of axis mitochondria decreased and phosphatidylethanolamine (PE) composition increased with seed maturation, with generally higher levels of PS and lower levels of PE in B73 as compared to A632. Phosphatidylcholine (PC) composition increased as seeds became tolerant to high-temperature desiccation during preconditioning. The ratio of PC/PE in axis mitochondria was higher in B73 than A632 and increased with time of preconditioning. In contrast, the ratio of PC/PE decreased as high-temperature desiccation tolerance was induced during seed maturation. Mitochondria from B73 axes had higher levels of oleic (18:1) and lower levels of linoleic (18:2) acid as compared to A632. Isolated mitochondria exhibited similar rates of State 3 respiration regardless of genotype, harvest moisture, or preconditioning time. No State 4 respiration was observed. Electron microscopy revealed similar mitochondrial ultrastructure in dry axis tissue, regardless of genotype, preconditioning time, or harvest moisture. The mitochondria from embryonic tissues appeared to be typical of those found in dry seed not directly damaged by high-temperature desiccation. Thus mitochondria are buffered from damage either by their osmotic location and/or other physiological mechanisms.