We present the first global simulations of the modulation of galactic cosmic rays by a three-dimensional solar wind with corotating interaction regions. The cosmic-ray transport equation is solved in a computed wind and magnetic-field model. The results show both the previously-neglected small-scale response to CIR's and global, drift-dominated, effects which are similar to previous models. Our model predicts a correlation between the local magnetic field and the rate of decrease of the cosmic-ray intensity which is similar to that observed. This is found to be due to inhibited diffusion. We suggest that such small-scale variations are local and that they do not change significantly the global cosmic-ray structure except, perhaps, near sunspot maximum. ¿ American Geophysical Union 1991