It has been suggested that inflamed airways may increase the exhaled breath temperature (EBT). We designed a simple instrument for EBT measurement and proven its precision, reproducibility and validity in asthma. Now we tested its utility as individual device to detect changes indicative of the control of asthma. We followed up 14 patients (9 female, age range 29-68 years) with uncontrolled asthma for 3 weeks after stepping up their anti-inflammatory treatment. Subjects were assessed upon inclusion in the study (visit 1, V1), after 1 (V2) and 3 weeks of treatment (V3) by visual-analogue scale (VAS), spirometry, blood and sputum eosinophils (Eos) and EBT. They also kept diaries with symptom scores (SS), peak expiratory flow (PEF) and EBT. Compared with V1, EBT decreased significantly at V2 and V3: from 35, 20Â°C [ 34 , 36÷35 , 56] (median [25 ÷ 75 interquartile range]) to 34, 70Â°C [34 , 48 ÷ 34 , 95] and 34,50Â°C [ 33 , 94 ÷ 34 , 91] respectively, p = 0.017. These changes paralleled the alteration in the other indices of asthma control. The mean weekly EBT and SS significantly decreased between week 1 and week 3 (p = 0.035 and 0.003 respectively), while PEF increased (p = 0.027). In conclusion, EBT is a useful indicator of asthma control to be used by physicians, but also by individual subjects at home.