Adult rats received one fifth of their measured daily food consumption until they lost 40% body weight. Some of these rats were then refed until they reached their initial body weight. We measured the following in fed, starved, and refed animals: (1) disaturated phosphatidylcholine (DSPC) content of lung tissue and of lavage fluid, (2) protein content of lung tissue and of lavage return, and (3) DNA and RNA content of lung tissue. In starved lungs, tissue and lavage DSPC content, total protein and RNA contents, and RNA/DNA ratios were significantly lower than in fed rats. After refeeding, DSPC values returned completely to normal, whereas protein, DNA, and RNA contents were significantly higher than in fed rats. The RNA/DNA ratio was similar in the fed and refed groups. Changes in lavage DSPC are consistent with the increased surface elastic forces in starvation and their return to normal with refeeding reported by us previously. It appears that starvation leads to a reduction in cell size without changes in cell number and that refeeding is associated with a more significant increase in cell number than in cell size.