Over a period of seven years, 30 horses were treated by surgical arthrodesis for lameness resulting from osteoarthrosis of the proximal intertarsal, distal intertarsal and tarsometatarsal joints (bone and occult spavin). Twenty-five horses were affected in one hock only and five were affected bilaterally. Four different techniques for achieving arthrodesis were used. Fourteen out of 18 horses (78 per cent) with involvement of the distal intertarsal and tarsometatarsal joints only and six out of 11 horses (55 per cent) in which the proximal intertarsal joint was also involved became sound following surgery. The status of one other horse, with involvement of the proximal intertarsal joint, is not known.