A histological and histochemical study of biopsy specimens from the Lapland reindeer antler indicated that the intercellular matrix of the cartilage that forms the partitions of longitudinal channels becomes calcified at virtually the initial stage of formation. The lacunae at the peripheries of the cartilaginous partitions are invaded by osteoblasts in a process comparable to endochondral ossification. The very centres of the partitions evidently become directly converted into bone without the presence of e.g. osteoclasts. The osseous partitions are remodelled by osteoclasts. The antler increases in diameter by periosteal apposition.