  Context: BL Lacertae objects have been the targets for numerous recent
multiwavelength campaigns, continuum spectral variability studies, and
theoretical spectral and variability modeling. A meaningful interpretation of
the results of such studies requires a reliable knowledge of the objects'
redshifts; however, the redshifts for many are still unknown or uncertain.
Aims: Therefore, we hope to determine or constrain the redshifts of six BL Lac
objects with unknown or poorly known redshifts. Methods: Observations were made
of these objects with the MDM 2.4 m Hiltner telescope. Although no spectral
features were detected, and thus no redshifts could be measured, lower redshift
limits were assigned to the objects based on the expected equivalent widths of
absorption features in their host galaxies. Redshifts were also estimated for
some objects by assuming the host galaxies are standard candles and using host
galaxy apparent magnitudes taken from the literature. Results: The commonly
used redshift of $z=0.102$ for 1219+285 is almost certainly wrong, while the
redshifts of the other objects studied remain undetermined.
