We compute all 3-point functions of the "universal" scalar operators contai
ned in the interacting, maximally supersymmetric CFTs at large N by using t
he AdS/CFT correspondence. These SCFTs are related to the low energy descri
ption of M5, M2 and D3-branes, and the common set of universal scalars corr
esponds 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 t
he d = 4, N = 4 super Yang-Mills theory and in the N = 8 SCFT3, related to
D3 and M2-branes, respectively.