Methionine restriction increases life span in rats and mice and reduces age-related accretion of adipose tissue in Fischer 344 rats. Recent reports have shown that adipose tissue mitochondrial content and function are associated with adiposity; therefore, the expression of genes involved in mitochondrial biogenesis and oxidative capacity was examined in white adipose tissue, liver, and skeletal muscle from Fischer 344 rats fed control (0.86% methionine) or methionine-restricted (0.17% methionine) diets for 3 months. Methionine restriction induced transcriptional changes of peroxisome proliferator-activated receptors, peroxisome proliferator-activated receptor coactivators 1alpha and 1beta, and some of their known target genes in all of these tissues. In addition, tissue-specific responses were elicited at the protein level. In inguinal adipose tissue, methionine restriction increased protein levels of peroxisome proliferator-activated receptor and peroxisome proliferator-activated receptor coactivator target genes. It also induced mitochondrial DNA copy number, suggesting mitochondrial biogenesis and corresponding with the up-regulation of citrate synthase activity. In contrast, methionine restriction induced changes in mitochondrial glycerol-3-phosphate dehydrogenase activity and stearoyl-coenzyme A desaturase 1 protein levels only in liver and uncoupling protein 3 and cytochrome c oxidase subunit IV protein levels only in skeletal muscle. No increase in mitochondrial DNA copy number was observed in liver and skeletal muscle despite an increase in mitochondrial citrate synthase activity. The results indicate that adiposity resistance in methionine-restricted rats is associated with mitochondrial biogenesis in inguinal adipose tissue and increased mitochondrial aerobic capacity in liver and skeletal muscle.