Lung deposition of 18 microg tiotropium administered via a dry-powder inhaler was investigated in 5 healthy subjects and patients with mild (n = 4), moderate (n = 6), and severe (n = 5) chronic obstructive pulmonary disease after 14 days of treatment with 18 microg tiotropium. On day 15, subjects inhaled 2 capsules of radiolabeled tiotropium, and lung deposition was assessed using gamma scintigraphy. Repeated plasma and urine collections were performed on days 14 and 15. Mean delivered dose from the dry-powder inhaler was 45.1%. Mean lung deposition relative to the delivered dose was 42% (19%, relative to nominal dose) with low intersubject variability (20%). Mean extrathoracic deposition was 57.5% (25.8%, relative to nominal dose). There were no significant differences in deposition among the subgroups. No significant correlation between individual tiotropium deposition and lung function was observed. These results suggest that all stages of chronic obstructive pulmonary disease may gain full therapeutic benefit from the drug.