  We present a method of determining lower limits on the masses of
pre-main-sequence (PMS) stars and so constraining the PMS evolutionary tracks.
This method uses the red-shifted absorption feature observed in some
emission-line profiles of T Tauri stars indicative of infall. The maximum
velocity of the accreting material measures the potential energy at the stellar
surface, which, combined with an observational determination of the stellar
radius, yields the stellar mass. This estimate is a lower limit owing to
uncertainties in the geometry and projection effects. Using available data, we
show that the computed lower limits can be larger than the masses derived from
PMS evolutionary tracks for M < 0.5 M_\odot. Our analysis also supports the
notion that accretion streams do not impact near the stellar poles but probably
hit the stellar surface at moderate latitudes.
