= 1 px. We are able to clearly detect the host galaxy in all the BL Lacs at low redshift (z$\leq$0.24). In the unresolved cases, the redshift is either high (PKS 1538+14; z = 0.605, PKS 0537–441; z = 0.896) or unknown but probably high (z$\geq$0.5; PKS 0048–097 and z$\geq$0.557; PKS 0118–272). Therefore, these sources are still consistent with being hosted by giant ellipticals. On the other hand, if their redshifts are lower, they may reside in sub–luminous hosts, which could account for the failure to detect absorption lines in the spectra of the latter two BL Lacs. In Fig. 2, we show the radial luminosity profiles of each BL Lac object, together with the best–fit models overlaid. In the Appendix, we compare our NIR photometry with previous studies, and discuss in detail individual BL Lacs, including comparison with previous optical determinations of the host galaxies. The results derived from the profile fitting are summarized in Table 2, where column (1) and (2) give the name and redshift of the object; (3) the bulge scalelength in arcsec and kpc; (4) and (5) the apparent nuclear and host galaxy magnitude; (6) the nucleus/galaxy luminosity ratio; (7) and (8) the absolute nuclear 