Extravascular lung water (EVLW) was estimated in 53 critically ill patients by the chest radiograph (CXR) and the thermal dye technique. The comparison between these two methods revealed a direct and positive correlation (r = 0.83, p less than 0.001). However, EVLW-values obtained by the thermal dye technique showed considerable overlap between cases of radiographic low grade pulmonary edema and we were able to identify several reasons for radiographic over- or underestimation of EVLW. In these patients EVLW-measurement by the thermal dye technique provides additional information, thereby probably influencing further treatment.