Spectroscopy of high-n Balmer line transitions provides a means of measuring n e and T e in recombining plasmas [J. L. Terry et al., Phys. Plasmas 5, 1579 (1998)]. The relative intensities of Rydberg series lines near the ionization limit are a sensitive diagnostic of T e , for T e <1.5 eV. Stark broadening of these same lines provides a measure of local n e and, with less accuracy, of T e . The accuracy of different theoretical models for Stark broadening [H.R. Griem, Spectral Line Broadening by Plasmas (Academic, New York, 1974); E. Oks, Stark Broadening of Hydrogen and Hydrogenlike Spectral Lines in Plasmas: The Physical Insight (Alpha Science International, Oxford, UK, 2006)] is evaluated by comparing values of n e and T e measured on DIII-D by divertor Thomson scattering (DTS) with those deduced from spectral profile analysis of Balmer series deuterium lines. In particular, the detailed dependence of line width on principal quantum number provides a sensitive metric for distinguishing which model best accords with experiment.