[en] A ⁶⁰Co source has been used to study the photoactivation of the 336 keV (T/sub 1/2/approx.4.3 h) isomeric level of ¹¹⁵In. In contrast to earlier investigations, we have considered the possibility of nonresonant processes and have developed a technique which allows us to distinguish between activation via the resonance fluorescence of the 1078 keV ¹¹⁵In level, and by nonresonant processes involving the 1172 and 1332 keV ⁶⁰Co photons. We have found that nonresonant processes are the dominant modes of activation. Although various possible mechanisms for the nonresonant excitation have been considered, none seem sufficiently strong to explain our results