  We investigate two chemical abundance calibrations for the narrow-line-region
(NLR) of active galaxies in terms of three easily observable optical
emission-line ratios, namely, [OIII]$\lambda\lambda$4959,5007/H$\beta$,
[NII]$\lambda\lambda$6548,84/H$\alpha$ and
[OII]$\lambda3727/$[OIII]$\lambda\lambda$4959,5007. The calibrations are
obtained from a grid of models on the assumption that the main process
responsible for the production of these lines is photoionization by a
``typical'' active galactic nucleus continuum. The chemical elements vary their
abundance together with oxygen, except nitrogen, which is assumed to be a
product of secondary nucleosynthesis. The calibrations are calculated for the
range $8.4 \le 12+log(O/H) \le 9.4$, and tested using NLR data for a sample of
Seyfert's and LINER's having HII regions in the vicinity of the nucleus. The
gaseous abundances of these HII regions have been determined in previous works,
and the NLR abundances are obtained on the assumption that they can be
extrapolated from those of the HII regions. The calibrations work very well for
the Seyfert's, giving abundance values which agree with those obtained from the
HII regions, and can thus be used for quick estimates of the chemical
abundances of the NLR's. For the LINER's, the calibrations give lower values
than those derived from the corresponding HII regions, suggesting that the
assumptions of the models do not apply for them, and that there are different
physical processes at work in the NLR of the LINER's.
