Abstract:Sixth generation of mutant maize seed homozygous for lysine plus threonine resistancewhich was derived from the resistant callus cultures has been harvested. The resistance could be inherited stably. The fertility, however, was very poor. The resistant homozygotes have been obtained by backcross of the wild type with the resistant plants (W77-R3019 ×R0), and their fertility could be parlty recovered after selection for the resistant plants from backcross progenies. Genetic analysis showed that the resistance inherited as a single dominant nuclear allele. All of the free amino acids except phenylalan inc in the homozygote are increased by 4 folds. and free essential amino acids by 5 folds which are higher than those in the wild types. Total amino acids increased by 5.53%. The dramatic increase (11 times) in free threonine adds up the total threonine by 17.73%. Difference of the protein content between the homozygote and wild type was not obvious. These results show that selection for the resistance to lysine plus threonine in maize and other cereals is probably very useful for improving their value of protein nutrition.