The effect of localized surface injection in a fully developed turbulent boundary layer was studied using hot wire techniques. Air was injected through a porous strip with a streamwise extent of about 3δ. As the flow recovered downstream from the perturbed boundary condition, a triple layer structure developed. Near the wall the flow quickly returned to standard flat plate conditions and no effetcs of the blowing could be detected in the outer layer over the downstream distance covered by the measurements (~ 23δ). In the intermediate layer considerable increases in all the turbulent stresses were found. However, the ratio between the stresses were found to remain the same as for the unperturbed layer, indicating that the flow structure was not affected. This was confirmed by the spectral energy distributions which were not changed. Therefore the intercomponental and spectral energy transfer appears to be sufficiently quick to account for the changes caused by the injection. Significant changes were however found in the production and dissipation of kinetic energy. These changes were compensated by modified diffusion rates.