The genetic transformation of mitochondria and chloroplasts has been an intractable problem. The newly developed "biolistic" (biological ballistic) process was used to deliver DNA into yeast cells to stably transform their mitochondria. A nonreverting strain, which is respiratory deficient because of a deletion in the mitochondrial oxi3 gene, was bombarded with tungsten microprojectiles coated with DNA bearing sequences that could correct the oxi3 deletion. Respiratory-competent transformants were obtained in which the introduced oxi3 DNA is integrated at the homologous site in the mitochondrial genome. Organelle genomes can now be manipulated by molecular genetic techniques in the same way as nuclear genomes.