  The decay properties of long-lived excited states (isomers) can have a
significant impact on the destruction channels of isotopes under stellar
conditions. In sufficiently hot environments, the population of isomers can be
altered via thermal excitation or de-excitation. If the corresponding lifetimes
are of the same order of magnitude as the typical time scales of the
environment, the isomers have to be the treated explicitly. We present a
general approach to the treatment of isomers in stellar nucleosynthesis codes
and discuss a few illustrative examples. The corresponding code is available
online at http://exp-astro.de/isomers/
