The electron structure, Stoner parameters, and exchange-enhanced local contributions to the spin susceptibility have been calculated for pure, Zn-doped, and Ni-doped (YBCO7) within the local density approximation, using a self-consistent T-scattering matrix method. It has been found that the Zn impurity causes a breaking of p - d covalence bonds in its vicinity, and gives rise to an island of reduced spin susceptibility and density of states at the Fermi level. This leads to the destruction of spin fluctuations near the impurity. The influence of Ni doping on the YBCO7 electron subsystem is much smaller than that of Zn doping. On the basis of the present results and the spin-fluctuation model, the effects of Zn and Ni doping on the critical temperature and NMR spectra of YBCO7 have been explained.