The regional pleural surface expansion of an excised dog lung was measured during high-frequency ventilation (HFV) using synchronized stroboscopic photography to stop lung motion at 20 evenly spaced intervals over a respiratory cycle during ventilation at 1 Hz with a volume of 100 ml, 15 Hz with 100 ml, or 30 Hz with 50 ml. The lungs were also photographed during quasi-static deflation. The pleural surface was marked with ink dots to form 84 approximately square figures. The side lengths and areas of each of the 84 "squares" were measured for each frame of each photo sequence. At 1 Hz and during the quasi-static deflation the lung ventilated nearly synchronously, although minor nonuniformities were noted on both small and large length scales. At 15 and 30 Hz, the lung expanded asynchronously and nonuniformly, with a 78% increase in surface expansion per 100 ml of tracheal tidal volume, as frequency was increased from 1 to 30 Hz. These nonuniformities in expansion suggest marked interregional airflow and elastic wave propagation in the parenchyma during HFV.