Gentamicin-impregnated polymethylmethacrylate beads were used in the treatment of infective synovitis in 12 horses and 10 cattle. They had either proved refractory to standard treatments (lavage, debridement, joint drainage and systemic antibiotics) or had evidence of osteomyelitis adjacent to a synovial cavity. All the animals were severely lame. All the cattle and six of the horses had radiological evidence of osteomyelitis in communication with a synovial cavity. The beads were placed intrasynovially under general anaesthesia and left in place for 14 days. One horse and one calf were euthanased owing to continued infective arthritis. The infection was eliminated from the other 20 cases and six of the horses returned to full athletic use. Eight of nine calves with E-type infective arthritis and osteomyelitis returned to their intended food production or breeding programmes.