Cross sections for the formation of seven fragments ranging from Na24 to Mn52 in the interaction of 18.5 GeV C12 ions and 400 GeV protons with Cu, Ag, Gd, Ta, Au, and U have been measured. After correction for the difference in bombarding energy, the results were used to test the factorization hypothesis. Enhanced fragment emission in C12 reactions was observed for all targets excepting copper. The magnitude of the enhancement and its dependence on target and product A are described. The variation of fragment yields with target A is examined. The neutron excess products obey modified Qgg systematics while the neutron deficient ones do not. The implications of these results for the reaction mechanism are considered. NUCLEAR REACTIONS Cu, Ag, Gd, Ta, Au, U [C12 and p, fragments (A=24−52)] TC12=18.5 GeV, Tp=400 GeV. Measured cross sections. Test of factorization, yield systematics. Gross γ-ray assay [Ge (Li)].