  We present a new computational scheme aimed at reducing the complexity of the
chemical networks in astrophysical models, one which is shown to markedly
improve their computational efficiency. It contains a flux-reduction scheme
that permits to deal with both large and small systems. This procedure is shown
to yield a large speed-up of the corresponding numerical codes and provides
good accord with the full network results. We analyse and discuss two examples
involving chemistry networks of the interstellar medium and show that the
results from the present reduction technique reproduce very well the results
from fuller calculations.
