  Multi-band near-infrared images of twelve BL Lacertae objects were obtained
with the 2.5m telescope at the Las Campanas Observatory in order to determine
the properties of their underlying host galaxies. Resolved emission was clearly
detected in eight of the lowest redshift targets (up to z~0.3), and was modeled
with a de Vaucouleurs r^{1/4} surface brightness law. We find that the
morphologies match the elliptical galaxy profiles well, and that the BL Lac
objects reside in large and luminous, but otherwise normal hosts -- consistent
with previous studies done predominantly at optical wavelengths. The median
absolute K-band magnitude of the galaxies in this study is -26.2, the average
half-light radius is 4.2 +/- 2.3 kpc, and their average integrated R-K color is
2.7 +/- 0.3 mag. These are well within the range of values measured previously
in the H-band by Kotilainen et al. and Scarpa et al. in a comparable number of
targets. Taking their data together with our results, we find a best-fit K-band
Kormendy relation of \mu_{e} = 4.3 log_{10} (r_{e}/kpc) + 14.2 mag arcsec^{-2},
virtually identical to that obtained for normal ellipticals. Finally, the
near-infrared colors determined for five galaxies (average J-K = 0.8 +/- 0.3
mag) are the first such measurements for BL Lac hosts, and match those expected
from old stellar populations at the BL Lac redshifts.
