A numerical investigation of space-time effects in the dynamic behavior of fast breeder reactors is presented. The basic approach is to compare results from point kinetics and time-dependent diffusion theory. The accuracy of point kinetics is determined for different approximations to the shape function used in calculating the initiating reactivity and feedback coefficients. Several space-dependent feedback models are studied. The importance of considering spatial effects that arise from two sources is shown. The first type consists of those induced by local reactivity perturbations. Usually, these can be adequately accounted for through the proper selection of a shape function. For example, it is found that when calculating rapid, localized ramp insertions, a good choice is the flux shape at prompt critical. The second type consists of those induced by feedback with strong space dependence. Spatial effects of this type are shown to be difficult to cope with when applying point kinetics.