The purpose of this study was to compare the efficacy and safety of the inhaled budesonide, sustained-release theophylline and montelukast, a leukotriene receptor antagonist, in patients with mild persistent asthma. In this single-center, randomized, parallel-group study that not designed blindly and placebo-controlled manner, 74 patients with mild persistent asthma were treated with either inhaled budesonide 400 microg once daily, oral montelukast 10 mg once daily, or sustained-release theophylline 400 mg once daily for 3 months. In all three treatment groups, improvements were attained in overall asthma control. Asthma symptom scores and supplemental beta2-agonist use were quite the same in all three treatment groups (P>0.05). Although inhaled budesonide group resulted in significantly greater improvements compared with the other two groups in the lung functions (P<0.05), the changes in FEV1 and PEF are within the baseline variability and there was no statistically significant difference among the groups when analyzed by treatment month (P>0.05). Exacerbations of asthma were experienced by 16% of the patients in the montekulast group, by 12.5% of the patients in the theophylline group, and by none of the patients in the budesonide group. The adverse event in each of the three groups was 12%, 16% and 16.7%, respectively. It is concluded that the most important clinical parameters do not point that one of the treatments is more effective than others. Treatment with inhaled corticosteroid is preferred, but sustained-release theophylline and leukotriene antagonists are alternative controller medications in mild persistent asthma.