In the present human study we evaluated a newly developed double-indicator-dilution densitometric system for the estimation of cardiac output (Q), central blood volume (CBV), and extravascular lung water (EVLW) by using indocyanine green and heavy water (2H2O) as indicators. Eighteen cardiopulmonary healthy patients scheduled for abdominal surgery were studied. A routine anesthesia procedure was used [thiopental (3-5 mg/kg), N2O (inspired fraction of O2 = 0.4), and isoflurane (end tidal 0.5-1.5%)]. Q, CBV, and EVLW were measured at seven defined data collection points: awake, anesthetized spontaneously breathing, apneic, mechanically ventilated with and without positive end-expiratory pressure, post-operatively anesthetized, and postoperatively awake. During the whole study EVLW (3.8 +/- 0.9 ml/kg) was stable in the presence of large fluctuations in Q (2.5-10.1 l/min) and CBV (0.8-2.4 l). We concluded that the method is versatile and of low invasiveness, allowing reliable on-line Q and EVLW data for repeated measurements in the clinical setting.