Young, adult, male albino mice lost almost half the liver total phospholipid during a 5-day fast. The liver weight also decreased in such a fashion that the phospholipid concentration remained approximately constant. The amounts of lecithin and cephalin decreased in proportion. The % P32 dose per mg of phospholipid increased markedly during fasting and, although the % P32 dose per mg lecithin is normally higher than that of cephalin, during fasting the values increased markedly for both fractions.