If an elevation of the right or left base of the lung is found on a chest x-ray film, differential diagnosis will have to consider the follwoing possibilities: 1. Elevation of the diaphragm, 2. Subpulmonary effusion and 3. Hernia of abdominal organs through the diaphragm. Suspicion of a subpulmonary effusion is prompted by the following x-ray findings: 1. Flattening of the costophrenic angle and elevation of the base of the lung. 2. Increased distance between "magenblase" (stomach bubble) and base of the lung. 3. Elevation of the lower margins of the lung, the apex being in the region of the lateral hemithorax. 4. Translucency of the margins of the diaphragm below the elevated base of the lung. 5. Absence of vascular shadoes behind the diaphragm on a wellexposed x-ray film. If one or several of these symptoms is seen, proof should be obtained by provoking issuing of the effusion by placing the patient in supine position or in lateral position on the affected side, and by trying to achieve visualization of the resulting condition.