The mitochondrial genome of four Epilobium species has been characterized by restriction analysis and hybridizations with gene probes from Oenothera. Mitochondrial DNA of Epilobium has a complex restriction fragment pattern and an estimated size of about 320 kb. All species exhibit specific restriction patterns. Plasmidlike DNA molecules of 0.3 kb to 1.2 kb are found in preparations of undigested nucleic acids of mitochondria from E. montanum, E. watsonii, and E. lanceolaturn. In contrast, the mitochondria ofE. hirsutum contain doublestranded RNAs of 2.7 kb. The location of the genes for cytochrome c oxidase subunits I and III on the mitochondrial DNA seems to be conserved in those species analyzed. However, the genes for subunit II of this complex, and for the alpha subunit of ATPase, are located on different restriction fragments in the mitochondrial genomes of certain species. The location of the COX II gene on different BamHI fragments in E. watsonii and E. lanceolatum has been used for the analysis of mitochondrial inheritance in reciprocal hybrids. Like the plastids, mitochondria are inherited maternally in Epilobium.