Entry of solar wind particles into Earth's magnetosphere is studied. Particles can move directly across an ''open'' magnetopause layer, where the magnetic field has a nonzero normal component (Bn≠0). Under the assumption that the Wal¿n relation holds near the open magnetopause, the solar wind particle influx can be expressed as Fn=n¿1/2&psgr;B/(&mgr;0mi)1/2, where n¿ is the average particle number density, &psgr;B is the open magnetic flux at the magnetopause, &mgr;0 is the permeability of free space, and mi is the ion mass. The total particle flux from the solar wind to the entire magnetosphere for a moderate negative value of IMF Bz is estimated to be ~7.0¿1028 s-1, although most of the particles leave from the antisolar end of the tail without being trapped. The peak flux through the dayside magnetopause is ~1.1¿1027 s-1, while the peak flux through the near-Earth tail magnetopause (‖ x ‖≤30RE) is ~3.0¿1027 s-1. The average particle flux through the dayside and tail magnetopause in the region with ‖ x ‖≤200RE is found to be ~7.9¿1027 s-1, which is comparable to the tailward particle flux (~7.1¿1027 s-1) observed at ‖ x ‖≂200--220RE in the distance tail. On the other hand, the total flux through the closed magnetopause (Bn=0) into the boundary layer in the region with ‖ x ‖≤200RE is estimated to be ~7¿1027 s-1, which is also comparable to the observed flux. For comparison, the ionospheric source contributes a particle flux of only 3--5¿1026 s-1. Thus, the ionosphere can be an important particle source for the inner magnetosphere (‖ x ‖≤30RE), but not for the entire tail or entire magnetosphere. ¿ American Geophysical Union 1989