This is a progress report on a collaborative effort to probe galaxy evolution by constraining the central mass-to-light ratios of distant field galaxies. Details can be found in a forthcoming paper (Rix, Guhathakurta, Colless & Ing 1996, RGCI). At the moment, the program is focused on the question of how over-luminous the abundant blue field galaxies at z ∼ 0.3 are (see Koo, K. and Kron, R. 1992), compared to galaxies of the same circular velocity and type at z ∼ 0. We have measured the integrated [OII] linewidths for a complete sample of distant blue galaxies to establish a linewidth-luminosity-color relation for this population and to compare this relation to the one for local galaxies. In addition, we explore practical strategies to obtain and analyze data so as to best relate the observable quantities (e.g. linewidths) to the physical quantities of interest (such as vcirc or M/L).