The disturbance of the bounary layer on a plate by tiny solid spheres is studied. The range of the particle dimensions is $ (Lbeing the length of the plate andReiis the background Reynolds number). Two model cases are analysed -- viscous and inertial-viscous. The forces that act on the solids inside the layer flow are calculated. The trajectories of particles with different radii are presented. The basic result is that fine solids are retained inside the boundary layer. This entrapment is maximal for particles whose dimensions are in the interval