Parental imprinting describes the phenomenon of unequivalent gene function based on transmission from the female or male parent. We have discovered parental imprinting of an allele of the dzr1 locus that posttranscriptionally regulates the accumulation of 10-kDa zein in the maize endosperm. The imprinted allele of MO17 inbred origin, dzr1 + MO17, conditions low accumulation of the 10-kDa zein and is dominant when transmitted through the female but recessive when transmitted through the male. Analyzing endosperms with equal parental contributions of dzr1 + MO17 ruled out the possibility that the unequivalent phenotype of dzr1 + MO17 was due to parental dosage imbalance in the triploid endosperm. Second-generation studies show that the dominant or recessive phenotype of dzr1 + MO17 is determined at every generation based on immediate parental origin with no grandparental effect.