Open lung biopsy is frequently performed as an emergency procedure in patients with undiagnosed bilateral diffuse pulmonary disease. In many situations, this procedure is undertaken in hemodynamically compromised or septic patients. An expeditious and simple technique to make an accurate diagnosis would be extremely advantageous. Biopsy of the lingular segment addresses most of these issues. Lingular biopsies, however, have been thought to be unreliable. The purpose of the present study was to evaluate the accuracy of lingular open lung biopsies in patients with bilateral diffuse pulmonary disease. Twenty consecutive patients with bilateral diffuse pulmonary disease underwent exploratory left thoracotomy when all noninvasive measures failed to arrive at a definitive etiology. Patients ranged in age from 24 to 79 with a mean of 52.6 years. There were five women and 15 men. Biopsy of the lingula was taken, as well as another area of similar lung involvement. Histopathologic results of the lingular biopsies correlated 100 percent with those from the other segments of the lung. The entire procedure, including rigid bronchoscopic examination, was routinely performed in less than one hour. In conclusion, lingular biopsies, relatively minor surgical procedures, are extremely accurate (100 percent) in making definitive diagnoses.