This study aimed to investigate the effect of treating patients with moderate asthma with formoterol on quality of life (QoL) and to compare several questionnaires in their ability to detect changes in QoL. In an eight month multicentre, randomized, placebo-controlled trial, patients with asthma using daily inhaled corticosteroids and beta2-agonists (> or = 5 inhalations x week(-1)) were randomized to 6 months treatment with formoterol 24 microg b.i.d. (by Turbuhaler) or a matching placebo. Patients recorded symptoms (maximal score 21) and peak expiratory flow (PEF) twice daily. QoL was measured with two asthma-specific questionnaires, the Asthma Quality of Life Questionnaire (AQLQ) and the Living with Asthma Questionnaire (LWAQ), and with two generic QoL forms, i.e. the Short Form 36 (SF36) and the Psychological and General Well-Being scale (PGWB) at randomization and after 6 months of treatment. Out of 110 patients studied, 56 received formoterol and 54 placebo. Mean baseline forced expiratory volume in one second was 65% predicted. Mean morning PEF was 369 L x min(-1). Mean total symptom score was 3.6. Morning PEF increased (26.8 L x min(-1), p=0.0001) and symptoms decreased (-1.23, p=0.012) in the formoterol group in contrast to placebo. QoL improvements were measured in the LWAQ total score (baseline 0.61, change -0.05, p=0.048) and the physical construct of the LWAQ (baseline 0.71, change 0.07, p=0.044). The AQLQ and the generic QoL instruments showed no significant changes. In conclusion, the improvement in quality of life reported after 6 months was very small and only reflected by the Living with Asthma Questionnaire.