An animal model for the study of osteoarthritis was described. The model involved the induction of degenerative articular lesions in New-Zealand-White-rabbits by the injection of nalidixic-acid (389082) (NA). Rabbits were injected with 1,000mg/kg NA daily for 3, 7, or 14 days. Hip, stifle, elbow, and shoulder joints were examined 14 days after the last injection. Gross abnormalities included blister like projections on the surfaces of the articular cartilage and erosions; frequency was dependent upon the joint and the duration of treatment. Light microscopic findings indicated progressive damage with increasing duration of treatment and included, in various degrees of severity, clefts in articular cartilage containing collagen strands, pyknotic nuclei in necrotic chondrocytes, cartilaginous flaps, and vesicles. Histochemical changes in the cartilaginous matrices within the articular lesions were seen at all stages of lesion development. Ultramicroscopic examination confirmed and characterized the degeneration and necrosis of the chondrocytes and demonstrated a decrease in density of collagen fibers in lesion areas along with fragmented fibers. The authors conclude that the quinolone arthropathy induced in rabbits in the present study is consistent with that seen in other experimental animals and represents a good model of osteoarthritis in humans.