  We detect emission from multiple low-excitation ro-vibrational transitions of
OH from the two Herbig Ae stars AB Aurigae and MWC 758 in the 3.0 - 3.7 micron
wavelength range (L-band), using the NIRSPEC instrument on Keck II. The inner
radius for the emitting region in both stars is close to 1 AU. We compare an
optically thin LTE model and a thin-wedge fluorescence model, finding
rotational temperatures of 650 - 800 K and OH abundances of 10^42 - 10^45
molecules for the two stars. Comparisons with current chemical models support
the fluorescence excitation model for AB Aurigae and possibly MWC 758, but
further observations and detailed modeling are necessary to improve constraints
on OH emission in different disk environments.
