Numerous case reports have shown the advantage of using bronchoalveolar lavage (BAL) in cytologic diagnosis of primary and secondary malignant neoplasms of the respiratory system. The aim of this study was to determine the usefulness of BAL in the diagnosis of peripheral, primary lung cancer. Of 1,864 patients referred to the Bronchological Department for endoscopic examination, 145 patients were studied: six with large cell lung cancer, 22 with adenocarcinoma, 15 with alveolar cell lung cancer, 40 with small cell lung cancer, and 62 with squamous cell lung cancer. In 94 patients (64.8 percent), BAL was diagnostic, revealing malignant cells. In 52 (35.9 percent) of these patients, the cytologic diagnosis agreed with the final pathologic diagnosis of the resected tumor. The result of BAL was affected by the type of cancer and size of the tumor. Highest yields were seen in adenocarcinoma (59.2 percent) and alveolar cell lung cancer (80 percent). The average size of the tumor in the group with correct cell typing was 4.9 +/- 1.8 cm; in patients with nondiagnostic BAL, the average size was 2.6 +/- 1.2 cm. BAL provided the highest (statistically significant, p less than 0.05) diagnostic yield (64.8 percent) in comparison with other sampling techniques: brush biopsy (29.8 percent), catheter biopsy (26.8 percent), and forceps biopsy (32.7 percent). The diagnostic yield of BAL and transbronchial fine needle aspiration biopsy (58.3 percent) did not significantly differ. BAL proved to be a valuable diagnostic tool in detecting peripheral, primary, pulmonary malignant neoplasms.