In a series of laboratory rats, pathologic and physiologic changes of the lungs were studied for 2 wk after intratracheal instillation of kerosene. The ratio of lung weight to body weight increased, indicating pulmonary congestion. Pathologically, 2 types of changes were seen: a generalized hyperemia and a focal bronchopneumonia. Physiologically there was an upward shift to the left of the static pressure-volume curve, with increases in total lung capacity of 35 to 40%. This was true whether air or saline was used as the inflating medium. All the changes described were maximal by 24 h after kerosene instillation and tended to return to baseline within 2 wk. Although static compliance of the lung increased, when normalized for total lung capacity there was no change, indicating that the shift was functionally equivalent to opening new lung units. We speculate that the leftward shift in the pressure-volume curve was due either to a reversible effect on lung elastin, or to changes in contractile elements located in lung parenchyma.