Five-week-old rats were fed on a diet containing phosphorus either at 0.3% (control diet) or at 1.5% (high p diet) for 21 days. Mitochondrial fraction was obtained from the kidney by the usual method. We investigated mitochondrial function as the indicator of mitochondrial swelling. When the substrate was not added to medium, mitochondria of rats fed a control diet or rats fed a high p diet showed swelling at 15% each in 60 minutes. When 5mM glutamate and 0.5mM malate were added, mitochondria of rats fed a control diet showed swelling. But the mitochondrial swelling was not observed in rats fed a high p diet and cytochrome C content in this group was lower than that of the control group. The possibility of mitochondrial functional disorder by excessive calcium was suggested
