It is shown that surface brightness parameters defined in terms of an isophotal radius are insensitive to galactic evolution, because the effects of luminosity evolution on the flux and isophotal radius almost cancel each other. Surface brightness parameters defined in terms of a metric radius are able to give fairly direct information on evolution, but only if the metric scale of each galaxy in the sample is determined by photometry of the galaxy itself. If, instead, a metric radius is estimated by means of a fiducial value of q/sub 0/, the brightness-redshift relation yields only a function of both evoluting and the unknown cosmological model, which is very similar to the function obtained from the Hubble diagram. (AIP)