The purpose of this study was to investigate the problem of mitochondrial biogenesis in rat liver. The approach consisted of isolating mitochondria from control, 6 day starved and 6 day starved‐5 day refed rats and comparing their DNA, RNA and protein content. This was performed by isolating the mitochondria by reorienting rate zonal centrifugation in sucrose gradients. It was found that six days of starvation resulted in a loss of 30% of the body weight, 55% of the liver weight, 40% of the mitochondrial protein, 60% of the mitochondrial RNA, but only 20% of the mitrochondrial DNA. It was also shown that refeeding of the rats for five days resulted in a restoration to normal or near normal levels in all the parameters measured. Further experiments employing the incorporation of ³H‐TTP into isolated mitochondria indicated that the maintenance of mitochondrial DNA was not the result of continuous DNA synthesis.