A high resolution (0.833° latitude by 1.25° longitude) AMIP run is compared with a standard resolution (2.5° by 3.75°) AMIP run. Both runs use HadAM2b, a recent version of the Hadley Centre GCM. ECMWF reanalysis data for the AMIP period (1979-1988), together with other climatologies, are used to validate the model runs. Increasing resolution increases the vertical motion, intensifies the hydrological cycle, reduces slightly the model's cold bias in the troposphere, shifts the westerly jets polewards and tends to increase the eddy kinetic energy and variability of the model. The high resolution simulation has less mid-latitude cloud, so altering the radiation balance. The detail in the precipitation field is generally improved at high resolution.