We demonstrate the feasibility of using laser spectrometry (LS) to analyze isotopically highly enriched water samples (i.e., delta2H < or = 15,000/1,000, 18O < or = 1,200/1,000), as often used in the biomedical doubly labeled water (DLW) method to quantify energy metabolism. The method is an important extension of a recently developed infrared laser direct absorption spectrometer. The measureme...