BACKGROUND Ipratropium and albuterol, combined in a single formulation, is widely used as three to four times daily maintenance therapy in COPD. This trial compared tiotropium, once daily, as a potential alternative to patients already taking the ipratropium/albuterol combination. METHODS 676 patients with moderate to very severe stable COPD (mean FEV(1)=39% of predicted) maintained on ipratropium/albuterol were randomized to receive over an 84 day period either tiotropium (18 mcg) each morning, or continue with ipratropium (26 mcg)/albuterol (206 mcg), 2 actuations 4 times daily, using a parallel group, double-blind, double-dummy design. Six-hour spirometry was assessed on study days 1, 22, and 84, along with safety assessments and other efficacy measures. RESULTS In terms of primary outcomes, mean trough FEV(1) at 84 days was larger in the tiotropium arm, as compared with the ipratropium/albuterol arm (difference=86 ml; 95% CI, 49 to 123 ml, p<0.0001). The mean FEV(1) AUC(0-6) at 84 days was also larger in the tiotropium arm (difference=17 ml; 95% CI, -21 to 56 ml), this difference being statistically non-inferior to the ipratropium/albuterol arm (p<0.001), but not statistically superior (p=0.37). Other efficacy measures were similar in the two groups. Lower respiratory adverse events were reported in 40 tiotropium patients vs. 52 ipratropium/albuterol patients. Safety reporting was otherwise similar. CONCLUSIONS Patients previously maintained on the ipratropium/albuterol combination taken four times daily can be switched to tiotropium once daily with the reasonable expectation of at least equivalent bronchodilation during daytime hours and superior bronchodilation during early morning hours.