MHD simulations have studied the evolution of an electric current system associated with fast reconnection development in three dimensions. The initial equilibrium is a one-dimensional antiparallel magnetic field with a current sheet (or plasma sheet) in the middle. Fast reconnection is initiated by a localized resistivity and spontaneously develops in a finite region of the current sheet, leading to an Alfv¿nic plasma jet. Ahead of the plasma jet the plasma sheet is notably compressed, forming a plasmoid which swells and propagates. In the fast reconnection region, notable plasma rarefaction occurs so that the plasma flow converges, whereas in the plasmoid, plasma is compressed so that the plasma flow diverges. The resulting velocity shear gives rise to a magnetic shear along the plasmoid boundary, which is directly related to a (positive) field-aligned current along the zero-order magnetic field. The field-aligned current is thus formed like a tube extending along the plasmoid boundary, and it becomes larger as the plasma compression in the plasmoid becomes larger. The fast reconnection development in three dimensions causes a drastic change in the overall current system to generate a redistribution of current. ¿ American Geophysical Union 1991