The rate coefficients for the reaction of OH with CO, k1, at pressures of 50--750 Torr from 220 K to 400 K, in He, N2, and air, are reported to be k1=(1.57¿10-13+3.54¿10-33¿[M>) cm3 molecule-1 s- with [M> in molecule cm-3. k1 increases linearly with the bath gas number density; this increase is independent of temperature. k1, at a given temperature and number density, is the same in N2, dry air, and mixtures of O2 (up to 49%) and N2. The presence of water vapor does not significantly alter k1 under atmospheric conditions. The uncertainty in our value of k1 is ¿15%, at the 95% confidence level, at any given [M> and temperature, which is smaller than the currently recommended uncertainty by a factor of four or more. Our k1 values are compared with previous data and their atmospheric implications are discussed. ¿ 2001 American Geophysical Union