[en] Cross sections are reported for x-ray production in targets of ₂₃V, ₂₉Cu, ₄₁Nb, ₇₃Ta, and ₇₈Pt by ₄₀Ar ions of 36.0, 56.4, 76.6, and 103 MeV. Because the targets were relatively thick, approx. 1 mg/cm₂, the data were corrected, using a novel approach, for projectile energy loss and x-ray attenuation in the targets. The cross sections so analyzed are compared with the predictions of the first Born approximation as well as with those of a more extensive treatment which includes energy loss, Coulomb deflection, perturbed stationary-state, and relativistic effects. The significant discrepancies between the data and this latter theory are atrributed primarily to the influence of multiple ionization on the x-ray emission probabilities