In alkaptonuric patients, cartilage, fibrocartilage and tendons are slowly impregnated by homogentisic acid. This leads to pigment deposition between and on the surface of collagen fibres (ochronosis) which hardens the tissues as in leather tanning, and can render them breakable. Ochronotic intervertebral discs show a tendency of calcification and ossification, which produces a characteristic radiological picture. Ochronotic cartilage is rather often split off in the weight bearing zones of the knee, shoulder and hip. This is followed by osteoarthrotic changes with a synovial reaction frequently leading to an osteochondromatosis. The labelling of the pigmented ochronotic cartilage thus can support a didactic demonstration of the nature of osteoarthrotic remodelling. It underlines that such remodelling consists mainly of non specific changes developing independently of the cause of the original cartilage lesion.