Superconducting transition temperatures Tc of sputtered Co/SC/Co trilayers and SC/Co bilayers with SC=Nb and NbTi were studied by the electrical resistivity and magnetic susceptibility. For a fixed Co layer thickness, Tc decreases with decreasing SC layer thickness. By applying a published model for the effects of pair breaking, the critical SC layer thickness dSC was deduced. The effect of interface roughness on Tc(dSC) is discussed from the viewpoint of the superconducting coherence length. © 2002 American Institute of Physics.