The diagnosis of interstitial pulmonary edema can be made only on the basis of the chest roentgenogram. This often is the first sign of left heart failure, which may be completely unsuspected clinically in the absence of alveolar edema. Kerley lines, or septal lines, are the most familiar roentgen sign of this condition. Other, more common findings include: perivascular and peribronchial cuffing, subpleural thickening, perihilar haze, and a generalized loss of translucency of the lung. Meticulous roentgen technic is essential for recognition of these subtle signs.