The nonchromosomal stripe (NCS) mutants of maize are a set of mitochondrial deletion mutants. In aerobic organisms, deletions of essential mitochondrial genes are lethal. Therefore, most plants carrying deletions of part of essential mitochondrial genes survive only heteroplasmically; that is, the plants contain mixtures of the deleted and normal mitochondrial genomes. The severity of the mutant phenotype depends on which mitochondrial gene is altered, which also influences the extent of homoplasmic tissues on the plants. NCS2 plants carry a partial deletion of the nad4 gene that codes for a subunit of complex I. Unlike animals, plants have additional enzymes that can partially compensate for the loss of complex I function. Kernels that are homoplasmic for the nad4 deletion mutation usually abort, although we report that homoplasmic mutant cultures can be initiated and maintained from immature embryos of such kernels. We also report the first example of a rare homoplasmic mutant NCS2 plant. The plant is very short, pale green, with a reduced number of narrow leaves. It is apparently male and female sterile. The possibility that the kernel that gave rise to this plant had a heteroplasmic endosperm is discussed.