AbstractThis report adds to the available information on comparative histology of mammalian bone and introduces a semi‐quantitative approach to its study. Bone samples consisted of large fragments of rib tibia and/or femur from humans, laboratory rodents and from animals that died at the Bronx Zoological Gardens. A total of 44 bone specimens representing six mammalian orders were available. Decalcified paraffin‐embedded 10 μm histological cross‐sections were examined at × 320. Qualitative observations were supplemented with measurements of the frequency and size distributions of Haversian and non‐Haversian canals. The relative distribution of lacunae was also ascertained. The standard textbook description of mammalian bone as consisting mainly of secondary osteons was not generally seen except in Primate (especially human) bone. Rats showed a few scattered osteon‐like structures, but bones of Marsupialia, Insectivora, Artiodactyla and Carnivora were entirely devoid of them. Generally, vascular bone with longitudinal canals was seen except in Lorisidae which showed a reticular type of bone. The distribution of primary longitudinal canals and the number of “filled” or “apparently empty” lacunae/unit area of bone varied both inter‐species and among different areas in the same bone. Large areas of acellular and non‐vascular bone were encountered in all specimens. This preliminary study revealed that species differences i bone microstructure involve the relative distribution of the same basic components which lend themselves to quantitative treatment. Comparative investigations of bone histology at many ontogenetic and phylogenetic levels should yield significant quantitative information in bone biology.