A series of large magnetic storms during the March--June 1991 period produced major changes in energetic particle fluxes in the magnetosphere. The most significant change was the addition of a semidurable belt of extremely energetic particles (Eel>15 MeV and Eprot>40 MeV) at 2.26.5 MeV and >1 MeV respectively). Cross-L motion rates for the first week after the storm sudden commencement of March 24, for the first month, and for the next 6 months have been obtained. The long- and short-term average rates of motion across L, ~6¿10-4 and ~3¿10-2 per day at L=2.0 to 2.3, are similar to radial diffusion rates obtained from the distribution functions of fission electrons (Farley, 1969) and of relativistic electrons after a major magnetic storm (Tomassian et al., 1972). It is inferred from the constancy in width of the belt that radial diffusion proceeded predominantly toward lower L. The long-term apparent decay rate for the particle flux intensity as seen by these instruments is a simple exponential in time: Nt=N0ek(1-t/t0), where k is 0.069. ¿ American Geophysical Union 1994