and k-corrected host galaxy absolute magnitude of the sample. All magnitudes were transformed into our adopted cosmology and into the H band. Based on the similarity of the BL Lac host galaxies to giant ellipticals (see discussion above), the transformation of published magnitudes to the H band was obtained assuming the following colours of giant ellipticals, computed from the literature values given in Table 4: V–H = 3.1, R–H = 2.5, I–H = 1.8, and H–K = 0.2. Finally, transformation from Gunn r filter (r–H = 2.8) was obtained from R–H = 2.5 (above) and r–R = 0.3, appropriate for low redshift ellipticals (Fukugita, Shimasaku & Ichikawa 1995).

[llrlll]{}\
\
& filter & N & $<z>$ & $<M_H(nuc)>$ & $<M_H(host)>^b)$\
\
(1) & (2) & (3) & (4) & (5) & (6)\
\
BL this work & H & 7 & 0.112$\pm$0.068 & -25.7$\pm$1.7 & -25.8$\pm$0.5\
& & & & &\
L\* Mobasher (1993) & K & 136 & 0.077$\pm$0.030 & & -25.0$\pm$0.2\
& & & & &\
BCM Thuan & Puschell (1989) & H & 84 & 0.074$\pm$0.026 & & -26.3$\pm$0.3\
BCM Aragon-Salamanca (1998) & K & 25 & 0.449$\pm$0.266 & & -27.0$\pm$0.3\
& & & & &\
BL 