Combined therapy with tiotropium and long-acting beta 2 agonists confers additional improvement in symptoms, lung function and aspects of health-related quality of life (QOL) compared with each drug alone in patients with COPD. However, the efficacy of combined therapy on walking distance, a surrogate measure of daily functional activity and morbidity remains unclear. The aim was, therefore, to quantify the benefit of this therapy on the six minute walk test. Secondary outcomes included change in lung function, symptoms, the BODE index and QOL. In a double-blind, crossover study, 38 participants with moderate to severe COPD on tiotropium were randomised to receive either formoterol or placebo for 6 weeks. Following a 2-week washout period, participants crossed over to the alternate arm of therapy for a further 6 weeks. Thirty-six participants, with an average age of 64.3 years and FEV1 predicted of 53%, completed the study. Combined therapy improved walking distance by a mean of 36 metres [95% CI: 2.4, 70.1; p = 0.04] compared with tiotropium. FEV1 increased in both groups (160 mL combination therapy versus 30 mL tiotropium) with a mean difference of 110 mL (95% CI: -100, 320; p = 0.07) between groups, These findings further support the emerging advantages of combined therapy in COPD. Australian New Zealand Clinical Trials.