  We report measurements of the surface impedance $Z_s=R_s+iX_s$ of
$(Pr_xY_{1-x})Ba_2Cu_3O_{7-\delta}$, $(x=0,0.15,0.23,0.3,0.4,0.5)$. Increasing
$Pr$ concentration leads to some striking results not observed in samples doped
by non-magnetic constituents. The three principal features of the $R_s(T)$ data
- multiple structure in the transition, a high residual resistance and, at high
$Pr$ concentrations, an upturn of the low $T$ data, are all characteristic of
the influence of magnetic scattering on superconductivity, and appear to be
common to materials where magnetism and superconductivity coexist. The low $T$
behavior of $\lambda (T)$ appears to change from $T$ to $T^4$ at large $Pr$
doping, and provides evidence of the influence of magnetic pairbreaking of the
$Pr$.
