  We have calculated the incident photon power density P_2 for which the
two-step induced emission rate from an isomeric nucleus becomes equal to the
natural isomeric decay rate. We have analyzed two-step transitions for isomeric
nuclei with a half-life greater than 10 min, for which there is an intermediate
state of known energy, spin and half-life, for which the intermediate state is
connected by a known gamma-ray transition to the isomeric state and to at least
another intermediate state, and for which the relative intensities of the
transitions to lower states are known. For the isomeric nucleus 166m-Ho, which
has a 1200 y isomeric state at 5.98 keV, we have found a value of P_2=6.3 x
10^7 W cm^{-2}, the intermediate state being the 263.8 keV level. We have found
power densities P_2 of the order of 10^{10} W cm^{-2} for several other
isomeric nuclei.
