Using spectra of normal emission line galaxies from the First Data Release of the Sloan Digital Sky Survey (SDSS) we have investigated the relations between the extinction C(Hβ) as derived from the Hα/Hβ emission line ratio and various global parameters of the galaxies. Our main findings include: C(Hβ) is linked with the galaxy spectral type and colour, decreasing from early- to late-type spirals. It also increases with increasing metallicity and is larger for more luminous galaxies and those with older stellar populations. The extinction of the stellar light is correlated with both the extinction of the nebular light and the intrinsic galaxy colours. The optical properties of the luminous infrared galaxies in our SDSS sample are very similar to those of our entire sample of SDSS galaxies. These results have implications for the determination of global star formation rates and total stellar masses in normal galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html