The influence of local blowing on a laminar boundary layer is analyzed numerically. Steady local uniform blowing is imposed in a cross flow through a thin slot. A regime diagram is constructed by varying the local blowing amplitude for three Reynolds numbers. As the local blowing amplitude is increased, the boundary layer flow begins to separate at a critical blowing rate, and on further increase of the blowing amplitude, spanwise vortex shedding occurs behind the slot. The simulation results show that in the regime where the flow is separated, the time-mean separation bubble length increases approximately linearly with the local blowing amplitude. In the vortex shedding regime, however, the time-mean separation bubble length decreases with increasing blowing amplitude. Other flow characteristics such as shedding frequency, the reattachment length, pressure coefficient, and near-wall mean velocity profiles are also examined. (C) 2006 The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.