We sought to determine if fasting (80% reduction of food intake for 72 h) diminishes airway or tissue disaturated phosphatidylcholine (DSPC) relative to alveolar surface area, or alters the lung response to overventilation. The lungs of fasted rats were lighter, but the size and recoil of saline-filled lungs, and the alveolar surface area of lungs fixed in glutaraldehyde, were the same in fed and fasted rats. In their airways fed rats had 0.32 +/- 0.01 microgram DSPC/cm2 of alveolar surface; fasted rats had 0.28 +/- 0.02 microgram DSPC/cm2 (P less than 0.05) (surface area determined at 20 cmH2O transpulmonary pressure). Fasted rats had 13% less tissue DSPC/cm2 alveolar surface than fed rats (P less than 0.01). After 1 h of mechanically produced overventilation the unequal amounts of airway, but not tissue, DSPC were eliminated and pulmonary compliance was similar in both groups. We conclude food reduction decreases the quantity of airway and tissue DSPC/cm2 of alveolar surface but does not increase lung recoil of spontaneously breathing rats (Gail, Massaro, and Massaro, J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 42: 88-92, 1977) or overventilated rats.