BL Lac host fainter than L$^*$. As found in the optical by Wurtz (1996), the BL Lac hosts have slightly, but not significantly lower luminosities in the NIR than nearby brightest cluster member galaxies (BCM; z = 0.07$\pm$0.03; M(H) = –26.3$\pm$0.3; Thuan & Puschell 1989). However, they appear significantly fainter than BCMs at higher redshift (z = 0.45$\pm$0.27; M(H) = -27.0$\pm$0.3; Aragon-Salamanca, Baugh & Kauffmann 1998).

Although the number of objects in this study is small, it is interesting to compare the NIR absolute magnitudes of BL Lac hosts to those of available samples of BL Lacs, RGs and FSRQs from the literature. These samples span a moderately large range in redshift from z$\sim$0.03 up to z$\sim$0.7. The average host galaxy magnitudes for the various samples are given in Table 5, and shown in Fig. 6. The BL Lacs in our study have host galaxies very similar in luminosity to those found by previous optical studies of BL Lacs if normal colors are assumed. Interestingly, there is good agreement between the BL Lac hosts in this study and the F-R II RGs of Taylor (1996), the only RG sample studied in the NIR and thus almost free from colour term 