The first 54 consecutive percutaneous aspiration biopsies of pulmonary lesions of an ongoing prospective trial performed in this hospital between July 1977 and March 1980 have been evaluated. The technique was found to be safe and provided a reliable and rapid diagnosis. An overall diagnostic accuracy of 83% was achieved. In malignant lesions a correct diagnosis was made in 85% of biopsies. These results are compared with other workers using the same technique and with fiberoptic bronchoscopy and sputum cytology. Aspiration is recommended as an excellent alternative to other more established techniques, particularly in the diagnosis of the peripheral lesion.