Currently available inhaled bronchodilators used as therapy for chronic obstructive pulmonary disease (COPD) necessitate multiple daily dosing. The present study evaluates the long-term safety and efficacy of tiotropium, a new once-daily anticholinergic in COPD. Patients with stable COPD (age 65.2+/-8.7 yrs (mean+/-SD), n=921) were enrolled in two identical randomized double-blind placebo-controlled 1-yr studies. Patients inhaled tiotropium 18 microg or placebo (mean screening forced expiratory volume in one second (FEV1) 1.01 versus 0.99 L, 39.1 and 38.1% of the predicted value) once daily as a dry powder. The primary spirometric outcome was trough FEV1 (i.e. FEV1 prior to dosing). Changes in dyspnoea were measured using the Transition Dyspnea Index, and health status with the disease-specific St. George's Respiratory Questionnaire and the generic Short Form 36. Medication use and adverse events were recorded. Tiotropium provided significantly superior bronchodilation relative to placebo for trough FEV1 response (approximately 12% over baseline) (p<0.01) and mean response during the 3 h following dosing (approximately 22% over baseline) (p<0.001) over the 12-month period. Tiotropium recipients showed less dyspnoea (p<0.001), superior health status scores, and fewer COPD exacerbations and hospitalizations (p<0.05). Adverse events were comparable with placebo, except for dry mouth incidence (tiotropium 16.0% versus placebo 2.7%, p<0.05). Tiotropium is an effective, once-daily bronchodilator that reduces dyspnoea and chronic obstructive pulmonary disease exacerbation frequency and improves health status. This suggests that tiotropium will make an important contribution to chronic obstructive pulmonary disease therapy.