Standardization of the solute output from the Wright nebulizer is necessary in nonspecific bronchial challenge to obtain reproducible results. Airflow and driving pressure are known determinants of the output. In an epidemiological study, in which day-to-day variations in room temperature occurred, we found the reproducibility of the output from a Wright nebulizer to be outside the range of acceptance. We have, therefore, examined to what extent ambient temperature and humidity might influence the output from three Wright nebulizers. The solute output was linearly correlated not only to flow (r = 0.98) and driving pressure (r = 0.90) but also to room temperature (r = 0.96). The mean output increased approximately 23% when room temperature was increased from 19 to 24 degrees C. This is equivalent to an increase in airflow of more than one litre. Ambient humidity did not influence the nebulizer output. When temperature was included in the calibration procedure, the coefficient of variation of the output decreased from 5 to 2%. This emphasizes the need for calibration of the Wright nebulizer with regard to ambient temperature as well as to airflow and pressure, especially in epidemiological field studies in which large variations of temperature are likely to occur.