An isotope ratio mass spectrometer will be acquired. The instrument will be part of a facility serving research scientists in regulatory biology, physiological ecology, and other areas of biology. The studies involve the use of doubly labeled water for measuring energy and material fluxes in free ranging animals. Very low enrichments of oxygen l8 and hydrogen 2 can be measured with the isotope ratio spectrometer. The ability to more accurately determine energy conservation and costs and benefits should have a significant impact on our understanding of the physiological ecology of animals.