The structural, magnetic and superconducting properties of the mixed compounds YBa2Cu3−xMxO7-y (M = Ni,Zn,Fe and Co) are reported. Values of y, determined by titration, are found to be dependent on the nature and amount of the doping. The range of solubility is greater for the Fe and Co compounds (x = 1) than for those with Ni or Zn (x = 0.3). The undoped material is orthorhombic and remains orthorhombic after substitution for Cu by Ni or Zn, whereas a tetragonal phase is observed when Fe, Co are substituted for Cu. DC resistance and AC susceptibility measurements show that Tc is depressed from 90K (x = 0) to 45K (x = 0.2) for both the Ni and Zn doped compounds and Tc is destroyed in the Fe and Co doped compounds when x reaches 0.4. We suggest that a valence of 2 be assigned to the Ni and Zn and 3 to the Fe and Co ions.