Useful information about hydration and the size of the body cell mass (BCM) can be obtained by monitoring changes in the amount of total body water (TBW) and its components, extracellular water (ECW) and intracellular water (ICW). A combined tracer dilution method with deuterium to measure TBW and bromide to measure ECW was used to assess changes in ICW (as a proxy for the BCM) and in the ECW/ICW ratio (an indicator of water distribution) over the course of recovery in nine severely burned children. During the acute phase of recovery, ICW losses averaged (mean +/- SD) 2.2 +/- 2.0 liters (P = .02) or 18.5 +/- 0.4%. During the rehabilitative phase, mean ICW increased by 3.4 +/- 3.7 liters or 31.9 +/- 14%. The ECW/ICW ratio varied widely both between patients and during the course of the study. During the acute phase of recovery, the mean ECW/ICW ratio increased from 1.06 +/- 0.15 liters to 1.20 +/- 0.14 liters because the ECW compartment had expanded relative to the ICW compartment. During rehabilitation, the ECW/ICW ratio decreased from 1.20 +/- 0.14 liters to 0.86 +/- 0.20 liters, with a recoup of ICW and continued ECW losses. Tracking ICW and the ECW/ICW ratio using the combined tracer dilution method is practical for monitoring BCM and water distribution in severely burned children. Taken together, the indices provide useful information about hydration and nutritional status in individuals recovering from severe burn injury.