Patients are treated with aerosolized PEN on an outpatient basis. The aerosol therapy is given by a respiratory therapist 5 times a week, for a total of 21 days of treatment. In addition, patients participate in two radioactive aerosol studies in which the patient inhales a radioactive gas while sitting with his/her back against a gamma camera. The resulting picture outlines the lungs. Then the gas is exhaled and the patient breathes an aerosol of PEN. This mist contains a single dose of PEN mixed with a small amount of radioactivity (99mTc-pertechnetate). The gamma camera determines where the particles deposit in the lungs. The radioactive exposure is equivalent to a typical x-ray of the ribs. Patients also undergo diagnostic bronchoscopy with lavage, and PFT. Blood is drawn to measure the blood level of PEN. Patients are followed (clinical exams and PFT's) for 6 months after the end of therapy. Prophylaxis for PCP is allowed during the 6-month follow-up.