Arthritis was experimentally induced in the intercarpal joints of a series of mature ponies by the intraarticular injections of 400 microgram of the polyene antibiotic filipin in 1 ml of dimethyl sulfoxide. Twelve consecutive weekly injections were administered and the ponies were euthanatized 4 weeks after the last injection of filipin was made. The ponies were exercised for 1 hour each day throughout the experiment. Articular cartilage specimens from 4 sites in each intercarpal joint were examined histologically and histo-chemically. For the histochemical examination, safranin O-fast green, Alcian blue in 0.4 M and 0.9 M MgCl2 and Alcian blue 0.9 M MgCl2-Van Gieson matrical staining techniques were used. Decalcified sagittal sections of selected carpi were also examined histologically. There was superficial fibrillation with chondrocyte necrosis in the articular cartilage specimens of the joints. This was accompanied by loss of histochemical staining of the amorphous intercellular matrix, which was attributed to loss of glycosaminoglycans. There were hypertrophy of remaining chondrocytes and chondrone formation. On examination of decalcified sections of carpi, both exostoses and marginal osteophytosis was observed. There was evidence of both intramembraneous and endochondral osteogeneses in the exostoses. The pathologic changes seen in the experimental model were compared with those observed in the naturally occurring disease. It was concluded that the changes were comparable with the early changes of degenerative joint disease in the horse.