  We have computed 500 chemical evolution models for the galaxy NGC 4303. With
the obtained evolutionary histories and a synthesis model we have also
calculated the spectral indices Mg2 and Fe5270. Fom the 500 models, by using a
chi-square technique, we obtain those reproducing the present day observations
within a confidence level of 95 %, reducing the number of possible models to
19. Only 6 of them are also able to reproduce the spectral indices radial
distributions with the same level of confidence. We conclude that this
technique of combining chemical with evolutionary synthesis models is a very
powerful tool, and, therefore, we propose to perform more observational
campaigns to obtain these and other spectral indices in spiral and irregular
galaxies.
