An experimental study of the two-dimensional laminartransitional boundary layer beneath a turbulent free stream is presented . It is shown that the mean velocity profiles develop a wavy shape prior to transition that contains local points of inflexion . These waviness is made clear by plotting the deviations of the profiles from the Blasius solution of the laminar bounary layer which is shown to be valid even for a turbulent free stream , Presently, a lecturer in the aeronautical department,