We have developed a direct insertion scheme for assimilating observed electron fluxes into a large-scale model of the inner magnetosphere. This data assimilation scheme is being developed for the Integrated Space Weather Prediction Model, but a simpler test model is used for the initial tests. The test model is a particle drift code that allows locally inserted electron flux measurements to propagate east along electron drift paths. Fluxes of ~40 keV electrons measured by geosynchronous satellites are used to constrain model electron fluxes as the model steps along in time, while similar measurements from separate spacecraft are used to test the procedure's effectiveness. In testing this scheme, two periods are used, April 21--23, 1988 (with three spacecraft about 120¿ apart in longitude), and March 28--April 4, 1996 (two spacecraft separated by 34¿). In these tests our data assimilation procedure modestly improved electron flux specification. The test results indicate that the data insertion scheme generally improved the electron flux specification within a region extending ~30¿ longitude east of the data-supplying satellite. However, only for quiet conditions does this direct insertion procedure improve the electron flux specification when the spacecraft are ~120¿ apart. ¿ 1999 American Geophysical Union