Forty healthy young subjects, ages 20 to 49 yr, underwent videobronchoscopy, mucosal biopsy, and bronchial lavage to evaluate the airway inflammation produced by habitual smoking of marijuana and/or tobacco. Videotapes were graded in a blinded manner for central airway erythema, edema, and airway secretions using a modified visual bronchitis index. The bronchitis index scores were significantly higher in marijuana smokers (MS), tobacco smokers (TS), and in combined marijuana/tobacco smokers (MTS), than in nonsmokers (NS). As a pathologic correlate, mucosal biopsies were evaluated for the presence of vascular hyperplasia, submucosal edema, inflammatory cell infiltrates, and goblet cell hyperplasia. Biopsies were positive for two of these criteria in 97% of all smokers and for three criteria in 72%. By contrast, none of the biopsies from NS exhibited greater than one positive finding. Finally, as a measure of distal airway inflammation, neutrophil counts and interleukin-8 (IL-8) concentrations were determined in bronchial lavage fluid. The percentage of neutrophils correlated with IL-8 levels and exceeded 20% in 0 of 10 NS, 1 of 9 MS, 2 of 9 TS, and 5 of 10 MTS. We conclude that regular smoking of marijuana by young adults is associated with significant airway inflammation that is similar in frequency, type, and magnitude to that observed in the lungs of tobacco smokers.