We present a parameterization for the tropospheric concentration of the hydroxyl radical (OH) which can be used to overcome the costs of solving kinetic equations in chemical tracer models. This parameterization accurately represents OH predicted by a full chemical mechanism. The 24-hour average concentration of OH is represented as a set of high-order polynomials in variables such as temperature, latitude, declination, and the concentrations of ozone, water vapor, carbon monoxide, nitrogen oxides (as a family), and hydrocarbons. The parameterization of OH consists of computer-written FORTRAN functions for an efficient computation of the polynomials. The parameterization of OH is publicly available. ¿ 2000 American Geophysical Union