The objective of this study was to determine the costs and effects of combined bronchodilator and anti-inflammatory therapy. In a 2.5-yr randomized controlled study, combined beta 2-agonist/corticosteroid therapy (BA + CS) and combined beta 2-agonist/anticholinergic therapy (BA + AC) were compared with beta 2-agonist/placebo therapy (BA + PL). Included in the study were 274 patients 18 to 60 yr of age with moderately severe obstructive airways disease. The main clinical endpoints were lung function, hyperresponsiveness, restricted activity days, and symptom-free days. The economic endpoints were the costs of health care utilization. Compared with BA + PL, BA + CS led to significant improvements in FEV1, PC20, and symptom-free days. BA + AC did not differ from BA + PL in this respect. The respective annual acquisition costs of BA + CS, BA + AC, and BA + PL were 532 US$, 277 US$, and 156 US$. Thus, BA + CS costs 376 US$ more than BA + PL. However, compared with BA + PL therapy, BA + CS led to statistically significant savings in other health care costs of about 175 US$ (95% CI from 46 to 303 US$). Thus, more than half of the additional costs of adding the inhaled corticosteroid are compensated for by a reduction in the costs of other health care services. Overall, inhaled corticosteroids lead to a small but net increase in health care costs of 201 US$ per patient per year.(ABSTRACT TRUNCATED AT 250 WORDS)