Micro-infrared spectroscopic measurements on single crystals of MgSiO3 perovskite document two pleochroic hydroxyl absorbance peaks at 3483 and 3423 centimeter(-1). These measurements were obtained with the use of a synchrotron infrared source for spectroscopy. These data are consistent with a trace hydrogen content of 700 +/- 170 hydrogen atoms per 10(6) silicon atoms in the nominally anhydrous MgSiO3 perovskite. When integrated over the volume of the lower mantle, this concentration is comparable to 12 percent of the mass of hydrogen in the Earth’s hydrosphere.