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57Fe and 151Eu Mossbauer spectroscopy as well as RF susceptibility measurements were applied to study the effects of Pr substitution either into the rare earth or into the Ba site in Eu1−x Pr x Ba2Cu3O7−δ and EuBa2−x Pr x Cu3O7−δ, respectively. Site mixing of Pr between the rare earth and Ba sites could be excluded by the utilization of 57Fe Mossbauer spectroscopy. It was found that there exists a correlation between the 151Eu isomer shift and the onset temperature of the superconducting transition independent of the location of Pr. RF susceptibility measurements provide an evidence for a difference in the magnetic moment of Pr substituted for the Eu or Ba sites. The obtained results can be explained by hole filling as the dominant effect of Pr substitution.