The reaction of methanol with a preoxidized Cu(100) surface in the temperature range of 90-200 K has been studied with reflection-absorption infrared spectroscopy (RAIRS). Methanol is found to form methoxy (CH3O) at or below 90 K. The ON stretch vibration at 3550 cm(-1) of a surface hydroxyl group (OH(ad)) appears as a small feature superimposed on the broad and much more intense OH stretch of adsorbed methanol at 3300 cm(-1). The assignment of the peak at 3550 cm(-1) to OH(ad) is supported by its shift to 3540 cm(-1) when preadsorbed O-18 is used in place of O-16. The peak due to OH(ad) disappears upon annealing to 150 K, presumably due to further reaction with methanol to produce additional methoxy.