The Algerian hedgehog (Aethechinus) has a diploid chromosome number of 48, similar to the European hedgehog species (Erinaceus) and to the long-eared Asiatic hedgehog. There are, however, differences in the size and structure of individual chromosomes. As compared with the European hedgehogs, which display three large blocks of distally located autosomal constitutive heterochromatin, there are only two such segments in the Algerian hedgehog. They are characterized by the following properties, of which some may apply to constitutive heterochromatin in general: heteropyknosis, late DNA replication, chromocenter formation, nucleolus-organizing capacity in the interphase nucleus, and asynchrony in the process of meiotic pairing. Deviating from findings in other species, the heterochromatic segments in the hedgehog fail to stain strongly following the conventional G- and C-banding techniques and do not show bright fluorescence after QM staining. However, when the preparations are subjected to extreme conditions of denaturation and reassociation, the heterochromatin shows marked C-banding. The different response to these dyes and to these staining techniques of various chromosomes and animal species may indicate the existence of several types of constitutive heterochromatin.