Nitric Oxide Therapy: Endotoxin is instilled in a lung (see above) and then nitric oxide a colorless, odorless, tasteless gas mixed with room air in a concentration of 40 parts per million, is given through a cushioned mask placed over the mouth and nose. (Some participants will be given the nitric oxide mixture and others will breathe only room air through the mask to test the effects of the nitric oxide on the lung inflammation.) The mask will be worn continuously for 6 hours and removed before repeat bronchoscopy with lavage, brushing and biopsy.