Adding a long-acting beta(2)-agonist (LABA) by dry powder inhaler (DPI) to tiotropium provides significantly increased and sustained bronchodilation in chronic obstructive pulmonary disease (COPD) patients over either product alone. To demonstrate similar benefits with a nebulized LABA, a placebo-controlled trial was conducted to evaluate the efficacy and safety of formoterol fumarate inhalation solution in subjects receiving tiotropium as a maintenance treatment for COPD. After a 7-14-day screening period using tiotropium 18 microg once daily, subjects with diagnosed COPD (> or = 25% to <65% predicted FEV(1)) were randomized to receive 20 microg formoterol fumarate inhalation solution twice daily for nebulization plus tiotropium (FFIS/TIO) or nebulized placebo twice daily plus tiotropium (PLA/TIO) for 6 weeks. Efficacy was assessed with spirometry at each visit (Day 1, Week 1, 3, 6), the transition dyspnea index (TDI), and St. George's Respiratory Questionnaire (SGRQ). Baseline characteristics were comparable, including mean FEV(1)% predicted. At Week 6, FEV(1) AUC(0-3) was 1.52 L for FFIS/TIO-treated subjects vs. 1.34 L for PLA/TIO-treated subjects (p<0.0001). The mean TDI scores in the FFIS/TIO and PLA/TIO groups were 2.30 and 0.16, respectively (p=0.0002). SGRQ did not change significantly with 6 weeks treatment, with the exception of FFIS/TIO improvements in symptom score vs. PLA/TIO (p=0.04). More PLA/TIO- than FFIS/TIO-treated subjects experienced AEs (39.7% vs. 22.9%), COPD exacerbations (7.9% vs. 4.5%), and serious AEs (3.2% vs. 1.5%). Nebulized formoterol fumarate in combination with tiotropium provided statistically and clinically significant improvements in bronchodilation and symptom control over tiotropium alone and demonstrated good tolerability.