Electron transfer flavoprotein (composed of alpha and beta subunits) is an obligatory electron acceptor for several dehydrogenases and is located in the mitochondrial matrix. Electrons accepted by electron transfer flavoprotein (ETF) are transferred to the main mitochondrial respiratory chain by way of ETF dehydrogenase (ETFDH). In humans, deficiency of ETF or ETFDH leads to glutaric acidemia type II, an inherited metabolic disorder that can be fatal in its neonatal form and is characterized by severe hypoketotic hypoglycemia and acidosis. We used cDNA probes for the Etfdh, Etfb, and Etfa genes to determine localization of these mouse genes to chromosomes 3, 7, and 13.