Intraarticular injections of orgotein, a metalloprotein with superoxide dismutase activity, did not ameliorate experimentally-induced osteoarthritis in the rabbit. Reduction of sulfate incorporation by cartilage of operated osteoarthritic knees with injection of saline-sucrose placebo and orgotein in saline-sucrose vehicle was observed. Repeated intraarticular injections of both orgotein in a sucrose-saline vehicle, and sucrose-saline placebo administered separately induced a severe synovitis in both osteoarthritic and normal knees.