The Kelvin-Helmholtz (KH) mode has long been considered for viscous interaction at the magnetospheric boundary but it is not expected to produce significant mass transport. The presented results indicate that the Kelvin-Helmholtz instability can indeed cause a transfer of mass into the magnetotail during times of northward IMF. The vortex motion of KH waves can generate a strongly twisted magnetic field with multiple current layers. Magnetic reconnection in the strong current layers inside the vortices can detach high density plasma filaments from the magnetosheath. This may explain observed high density and low temperature filaments in the magnetosphere and the correlation of the plasma sheet density and the solar wind density. We present a two-dimensional study of reconnection and mass transport in KH vortices depending on magnetosheath and magnetospheric plasma and field properties. For individual waves the average mass entry velocities is determined to be several km/s. ¿ 2001 American Geophysical Union