An earlier formulation rougly relating core-polarization effects for different external fields, electromagnetic ($p,{p}^{\ensuremath{'}}$), ($\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}$), etc., through a 2 \ifmmode\times\else\texttimes\fi{} 2 core-polarization matrix has been generalized to include chargeexchange reactions under the assumption that the isospin of the nuclear states is pure. The pure isovector field of the direct charge-exchange reaction to an excited-analog state has both an isovector and an isoscalar field for the model space as in inelastic scattering. A crude schematic representation of the giant resonances, virtually excited by interaction with the model space and responsible for the core polarization, is used to estimate the effect on the core-polarization parameters of imposing isospin conservation. The results of the earlier formulation are changed only slightly. Direct excitation of giant-quadrupole resonances in $^{208}\mathrm{Pb}$ by ($p,{p}^{\ensuremath{'}}$) and ($n,p$) are compared. Energy shifts of the ${T}_{g}$ and ${T}_{l}$ isovector giant-quadrupole resonances are compared with the corresponding dipole shifts.NUCLEAR REACTIONS Low lying ${0}^{+}\ensuremath{\rightarrow}{2}^{+}$ transitions; extension of core-polarization effects to include charge exchange by application of isospin conservation. Giant-quadrupole transition rates and isovector splitting estimated.