The major thrust of the Tully-Fisher (TF) surveys of distant galaxies is the measurement of linewidths rather than mere redshifts or colors. Linewidths are a measure of galaxy mass and should therefore be a more stable indicator of size than galaxy brightness, which can be badly affected by luminosity evolution. Masses may provide the best way to relate galaxies at different epochs, but for such a program to work, we must control systematic effects that could bias linewidth measurements at high

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... redshift and skew comparisons with local Tully-Fisher calibrations. Potential sources of confusion in TF studies of galaxy structure and evolution include central or extended star bursts, infalling gas, turbulence and outflows, dust extinction, calibration of emission linewidths, and improper application of local TF calibrations to high redshift galaxies.