In order to determine the pathogenesis of ulcerative lesions of the articular cartilages in Japanese Black cattle, tissue samples of the ulcerative lesion, marginal portion of the ulcer, macroscopically normal portions and synovial membranes were histopathologically examined by light microscopy, scanning electron microscopy and contact microradiography. The results are summarized as follows: (1) In the ulcerative lesions, degeneration and complete destruction of articular cartilage and its replacement with a proliferation of myelogenic connective tissue were observed. (2) In macroscopically normal portions, fissures of the articular surface and changes of the trabecular pattern in subchondral bone were present. (3) In the marginal portions of the ulcerative lesions, evidences of the repair process such as connective tissue growth from subchondral bones and articular cartilages were seen. (4) In synovial membranes, no pathological findings were observed. And (5) among the above mentioned changes, no inflammatory findings were seen. In conclusion, the ulcerative lesions of bovine articular cartilage may be regarded as the early stage of osteochondrosis to osteoarthrosis since the findings such as non-inflammatory destruction or degeneration and remodeling of the joints are characteristics of the latter.