Malic enzymes were studied in skeletal muscle from seven patients with Friedreich's ataxia (FA) and nine controls. Muscle contained three different malic enzymes. There were two strictly NADP+-dependent enzymes, one in the cytosol and one in mitochondria. These two enzymes are not allosteric. In FA muscle, activity of the mitochondrial NADP+-linked enzyme was significantly low and the cytosol NADP+-linked enzyme was significantly increased. A third malic enzyme, NAD+(P)-dependent, was found in the mitochondrial fraction. That enzyme had allosteric properties, and its activity was about the same in FA and control muscle.