A better insight into bone pathophysiology is required for a full understanding of the mechanisms leading to bone loss in humans. Animal models of bone disease appear to be the most valuable for this purpose. Certain differences in bone metabolism exist between various species. Non-human primates are the most human-compatible animal species, whereas dogs appear to be most appropriate among small laboratory animals. However, the high cost of studies on primates and dogs restricts the number of animals examined. The rat is the most frequently used animal. Many similarities have been observed in bone metabolism of humans and rats. Like humans, rats also lose bone with aging, and in some parts of the rat skeleton bone remodelling occurs. However, bone metabolism in rat is mainly characterized by growth and modelling, which makes the rat model completely appropriate for studies of juvenile osteopenias. Characteristics of animal models of osteopenias should be comprehensively investigated in order to render the study results completely, or with known exceptions, comparable to the corresponding processes in humans.