Osteochondrosis is an impaired focal endochondral ossification which appears as a cartilage retention in the subchondral bone of growing pigs. The normal differentiation of chondrocytes does not occur and the matrix calcification is restricted. The present investigation has compared the content of selected macromolecules in the cartilage matrix of the normal articular and epiphyseal growth cartilage with the osteochondrotic cartilage, using a peroxidase-antiperoxidase (PAP) immunocytochemical method at light microscopical level. Some of the non-collagenous macromolecules (fibromodulin, large aggregating proteoglycans, fibronectin, 100-kDa subunit protein and 148-kDa protein) were conspicuously prominent within the osteochondrotic cartilage, compared to the matrix of the "normal" resting, proliferative and hypertrophic regions. This indicates that the chondrocytes in the osteochondrotic cartilage do not modify their surrounding matrix adequately, thus precluding normal calcification.