We use the photoionization code MAPPINGS Ic to model optical emission-line ratios of the extended emission-line regions of 24 Seyfert galaxies. Although most line ratios can be reproduced by varying the ionization parameter, gas density and/or the shape of the ionizing continuum, the ratio [NII]λλ6548,84/[OII]λ3727 can only be reproduced if we allow for a range of oxygen abundances of 0.5≤ (O/H)/(O/H)$_{\odot} \leq$ 3 for the whole sample. We propose a calibration to obtain (O/H) in terms of [NII]/[OII]. Also, in order to reproduce the emission-line spectra beyond 2 kpc from the nucleus, we had to introduce the contribution from hot stars to the ionizing spectra. We conclude that this is due to an increasing contribution of HII regions with distance from the nucleus to the emission-line regions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html