Solar wind measurements are used to predict the MeV electron radiation belt flux at the position of geostationary orbit. Using a model based on the standard radial diffusion equation, a prediction efficiency of 0.81 and a linear correlation of 0.90 were achieved for the years 1995--1996 for the logarithm of average daily flux. Model parameters based on the years 1995--1996 gave a prediction efficiency and a linear correlation for the years 1995--1999 of 0.59 and 0.80, respectively. The radial diffusion equation is solved after making the diffusion coefficient a function of the solar wind velocity and interplanetary magnetic field. The solar wind velocity is the most important parameter governing relativistic electron fluxes at geostationary orbit. The model also provides a physical explanation to several long standing mysteries of the variation of the MeV electrons. ¿ 2001 American Geophysical Union