The optical absorption spectra of nominally pure and rare-earth-ion-doped (Ho3+ or Er3+) calcium aluminoborate (cabal) glasses were measured from 190 to 900 nm before and after gamma -ray irradiation. The induced absorption spectra, calculated as the difference between the spectra of the irradiated and the unirradiated glasses, exhibit the characteristic absorption bands caused by the respective rare-earth ions. The intensity of the induced bands depends on the rare-earth oxide content. The response of the cabal glass to gamma -ray irradiation is related to the formation of color centers associated with the intrinsic defects in the lattice structure of the cabal glass. The rates of formation and annihilation of the color centers are believed to approach saturation or equilibrium with prolonged irradiation.