Background: Asthma is a chronic inflammatory disease of the airways. Inhaled corticosteroids are very important in anti-inflammatory treatment, but to a great extent they cannot control asthma alone. In addition to corticosteroids, long-acting 2 agonists and leukotriene antagonists are used for asthma control. Objective: In this study, the effect of the addition of formoterol and montelukast on asthma control in patients with moderately persistent asthma who were symptomatic while using a low dose of inhaled budesonide was compared. Methods: At the beginning of the study, 40 symptomatic patients with moderately persistent asthma used 400 mug/day budesonide for a 4-week training period, and were then divided randomly into two groups, each composed of 20 persons. For the first group's treatment regime, inhaled formoterol ( 9 mug) twice a day was added, and for the second group's treatment regime, one-dose oral montelukast (10 mug) was added. These patients were followed up for 8 weeks. The patients' peak expiratory flow (PEF) values measured in the morning and at night, changes in PEF, forced expiratory volume in 1 s, asthma symptom score and the symptom-relieving therapy used during the 12-week study period were recorded and evaluated in the clinic at the very beginning and at the end of each period. Results: Before the study, the morning PEF value of the group for whom formoterol was added to budesonide (FB) was 266.3 +/- 59.3 liters/min, and in the group for whom montelukast was added to budesonide (MB), it was 262.8 +/- 53.8 liters/min ( p > 0.05). After the 8-week treatment period, the morning PEF values were found to be 320.5 +/- 54.4 liters/min in the FB group and 293.3 +/- 52.4 liters/min in the MB group; at the end of the study, it was seen that although there was an increase in morning PEF of 54.2 +/- 15.2 liters/min in the FB group, there was an increase of only 30.5 +/- 25.3 liters/min in the MB group (p < 0.0001). Before the study, night PEF values were 287 +/- 56.6 liters/min in the FB group and 283 +/- 48.5 liters/min in the MB group (p > 0.05). At the end of the treatment, the night PEF values were found to be 331.5 +/- 56.1 liters/min in the FB group and 310 +/- 53.1 liters/min in the MB group. At the end of the study, it was observed that although there was an increase in night PEF of 44.5 +/- 23.3 liters/min in the FB group, there was an increase of only 27 +/- 24.1 liters/min in the MB group (p < 0.001). Although asthma symptom scores and the use of symptom-relieving drugs showed similarities between the two groups at the beginning of the study, after treatment, the FB group had better results than the MB group with respect to these two parameters (p < 0.0001 for both). It was also seen that the two treatments are tolerated equally well. Conclusion: FB treatment, which causes a considerable improvement in lung function, showed better asthma control than MB treatment in patients with moderately persistent asthma. Copyright (C) 2004 S. Karger AG, Basel.