The reaction of the hydroxyl radical (OH) with the stable carbon isotopes of methane has been studied as a function of temperature from 273 to 353 K. The measurd ratio of the rate coefficients for reaction with 12CH4 relative to 13CH4 (k12/k13) was 1.0054 (¿0.0009 at the 95% confidence interval), independent of temperature within the precision of the measurement, over the range studied. The precision of the present value is much improved over that of previous studies, and this result provides important constraints on the current understanding of the cycling of methane through the atmosphere throught he use of carbon isotope measurements. ¿ American Geophysical Union 1990