It is generally stated that the process of cartilage calcification and ossification is the same in the physeal (primary growth center) and epiphyseal (secondary growth center) growth plates. Reexamination of osteophyte growth led to the proposal that these growth plates differ. This proposition was tested by examining rabbit and human material from both sites before and after maceration; both tissue preparations were processed for light microscopy, and the macerated tissues were also studied by scanning electron microscopy (SEM). The physis showed the well-recognized, longitudinal calcified tubal structures in which capillaries make direct contact with and resorb the nonmineralized, transverse septal cartilage. In the epiphysis, the transverse septal cartilage was also mineralized, producing a continuous calcified sheet, perforated only by a limited number of channels and susceptible only to osteoclastic removal. This variation in mineral distribution modifies the way in which the primary spongiosa is formed during growth.