We compared nonbronchoscopic bronchoalveolar lavage (NB-BAL) with open lung biopsy to determine the etiological diagnosis of lung infiltrates in patients requiring mechanical ventilation. NB-BAL was performed via a cuffed reusable 7F catheter generally used for right heart catheterization (BAL-C). In 13 patients, BAL-C and open lung biopsy were performed in the same lobe immediately after death when the ventilator was still functioning. No organism was cultured from BAL-C cultures when histopathologic examination of the lung showed no pneumonia and lung culture isolated no organism. Among the 10 positive BAL-C cultures, lung biopsy showed histologic pneumonia in 9 cases. Among these 9 pneumonia cases, 14 organisms were isolated in lung cultures and BAL-C correctly identified the causative agent in 13 cases. BAL-C appears to be an effective and safe procedure in the diagnosis of pulmonary infections in patients under mechanical ventilation who have previously received antibiotic therapy.