We present high-resolution imaging of the BL Lac objects 1ES 0229+200 (z = 0.14), Markarian 421 (z = 0.031) and the prototype BL Lac (z = 0.069). Our goal is to study the properties of the host galaxies of this enigmatic sources and to compare them with their non-actice counterparts. The observations were carried out with the Nordical Optical Telescope (NOT) at La Palma under sub-arcsecond seeing conditions (FWHM < 0.″8). The surface brightness profiles of the host galaxies were analyzed as described in Bender and Möllenhoff (A&A, 177, 71 (1987)). After masking the disturbing field stars/galaxies isophotes were fitted by ellipses down to 20.5 mag/arccsec2 in Markarian 421, 23.5 mag/arcsec2 in BL Lac and 25.5 mag/arcsec2 in 1ES 0229+200. Additionally, we analyzed the surface brightness profile of the companion of Markarian 421.

The surface brightness profiles of the host galaxies were analyzed as described in Bender and Möllenhoff (A & A, 177, 71 (1987)). After masking the disturbing field stars/galaxies isophotes were fitted by ellipses down to 20.5 mag/arccsec2 in Markarian 421, 23.5 mag/arccsec2 in BL Lac and 25.5 mag/arccsec2 in 1ES 0229+200. Additionally, we analyzed the surface brightness profile of the companion of Markarian 421.