Posteroanterior and lateral chest radiographs were obtained in 19 healthy subjects after routine instruction. Immediately afterwards, repeat films were obtained with the subjects vigorously coaxed to maximal inhalation. Total lung capacity was measured from both sets of radiographs. Normal subjects inhale to 95.5% +/- 3.8% (SD) of total lung capacity during routine chest radiography. Routine chest radiographs will provide useful total lung capacity measurements. Old chest radiographs, in addition to frequently being a mandatory part of the clinical evaluation of patients with chest problems, may provide the only antecedent information about lung function (total lung capacity).