Several samples of disk galaxies have been collected in order to study, in each of them, the relation between the blue total corrected absolute magnitude and the absolute corrected isophotal diameter. These luminosity-diameter relations have been compared to detect a possible dependence on the density of the galaxy environment. No significant differences have been found among the several relations, especially if selection criteria relative to the various samples are taken into account. This result is in disagreement with several previous claims.
