We compute all 3-point functions of the ``universal'' scalar operators contained in the interacting, maximally supersymmetric CFTs at large N by using the AdS/CFT correspondence. These SCFTs are related to the low energy description of M5, M2 and D3-branes, and the common set of universal scalars corresponds through the AdS/CFT relation to the fluctuations of the metric and the magnetic potential along the internal manifold. For the interacting (0,2) SCFT₆ at large N, which is related to M5-branes, this set of scalars is complete, while additional non-universal scalar operators are present in the d = 4, N = 4 super Yang-Mills theory and in the N = 8 SCFT₃, related to D3 and M2-branes, respectively.