BACKGROUND: Pharmaceutical industry-sponsored research has been shown to be biased toward reporting positive results. Frequent industry participation in trials assessing the efficacy of inhaled corticosteroid (ICS) and long-acting beta2-agonist (LABA) combination treatment makes assessing industry influence difficult and warrants an assessment of specific potential publication bias in this area.OBJECTIVE: To describe the frequency of industry involvement in ICS/LABA trials and explore associations among significant outcomes, type of industry involvement and type of primary outcome.METHODS: A systematic review of trials comparing ICS/LABA combination therapy with ICS monotherapy for asthma was conducted. Data concerning the type of industry sponsorship, primary outcome and statistical results were collected. Comparisons between type of sponsorship and significant results were analyzed using Pearson’s χ2 test and relative risk.RESULTS: Of 91 included studies (median year of publication 2005 [interquartile range 1994 to 2008]), 86 (95%) reported pharmaceutical involvement. Author affiliation was reported in 49 of 86 (57%), and 19 of 86 (22%) were industry-reported trials without full publications. The remainder were published journal articles. Studies with a first or senior author affiliated with industry were 1.5 times more likely to report statistically significant results for the primary outcome compared with studies with other types of industry involvement. Pulmonary measures were 1.5 times more likely to be statistically significant than were measures of asthma control.CONCLUSIONS: The potential biases identified were consistent with other research focused on author role and industry involvement, and suggest that degree of bias may vary with type of affiliation.