BACKGROUND: Exhaled breath temperature (EBT) is a new noninvasive method for the study of inflammatory respiratory diseases with a potential to reach clinical practice. However, few studies are available regarding the validation of this method, and they were mainly derived from small, pediatric populations; thus, the range of normal values is not well established. The aim of this study was to measure EBT values in an Italian population of 298 subjects (mean age, 45.2 +/- 15.5 years; 143 male subjects; FEV1, 97.2% +/- 5.8%; FVC, 98.4% +/- 3.9%) selected from 867 adult volunteers to define reference values in healthy subjects and to analyze the influence of individual and external variables on this parameter. METHODS: EBT was measured with an X-halo PRO device to different ambient temperature ranging from 0 degrees C to 38 degrees C. RESULTS: We report reference values of EBT in healthy white subjects who had never smoked. EBT values were strongly influenced by the external temperature and to a lesser extent according to sex. CONCLUSIONS: In a large population of healthy subjects who never smoked, these data provide reference values for measuring EBT as a basis for future studies. Our results are contribute to the promotion of EBT from "bench" to "bedside."