[en] The infrared absorption technique, which we have developed for the continuous analysis of deuterated water in circulating blood, provides a versatile method for studying the movement and the distribution of water in all organs to which entry and exit are accessible. The interest attached to the early diagnosis of pulmonary oedema and following the results of its medical treatment, has led to the development (by R. Capitini, CEN Saclay) of a double spectrophotometer of original design which enables heavy water and Indocyanine Green to be measured directly at 4 μ and 0,8 μ respectively in a single cell. This elegant system avoids some drawbacks of two spectrometers mounted in series and leads to an increased performance. We have shown the validity of the method for determining the cardiac output and the pulmonary extravascular water in the course of numerous experiments on 27 rats and 32 human subjects