[en] We report on the production of intermediate and high mass muon pairs in p-A and S-U collisions, as measured by the NA38 experiment at the CERN SPS. The ratio between ψ' and J/ψ cross-sections is found to be constant in p-A interactions but decreases from p-A to S-U and as the released transverse energy, E_T, increases. While the p-A intermediate mass continuum is well explained by the superposition of Drell-Yan and charm contributions, the signal observed in the S-U data is larger than the linear extrapolation of the proton-nucleus results. No correlation is seen between dimuon and direct photon production. (orig.)